Car overheats after driving for 30 mins?

My 2005 Honda Civic LX had a coolant leak. Replaced the radiator, thermostat, and hoses. I filled the system up with 50/50 and water. Bled it completely of air and everything seems fine until I drive for about 30 mins straight.

I'm positive that it isn't a head gasket problem because I have no coolant in my oil or vice versa. I have no signs of leaks, but gauge begins to move up after a long drive and overheats.

I'm completely lost because I have no leaks whatsoever, No air is in the system because it was properly bled (a few times at that), and coolant is full! What else could it be? My water pump doesn't show any signs is wear but my only guess is that my thermostat is faulty or water pump is weak. Any ideas?

How many times did it do this? Because once could easily be air despite your efforts. Ruling that out, the thermostat is likely. But there's no reason to guess about this.
When cool enough to remove the radiator cap safely, do that then start up the engine and let it warm up. The fluid will be visible in the radiator and it will not be doing much except expanding. It takes a long time for the thermostat to open. When it does you will see the coolant rushing by. If it never opens, there's your problem. You can also determine this simply by feeling the upper hose. If you see vigorous flow then the water pump is okay. It is always possible that the radiator needs flushing or replacement. A ref\verse flush for your engine might work, as can some radiator flush chemical. All depends on what is wrong.

Just remove the thermostat for a drive to see if that's a problem. And cheap, lower radiator hoses can collapse from suction if you didn't put the spring in.

You don't need fluid mixing to prove a head gasket failure. Honda's fail at the fire ring and compression blows past the cylinder wet liner into the water jacket. The excess pressure in the jacket prevents coolant flow and the engine over heats.

Many decent comments given. Especially when cold engine rad cap off. As engine warms on idle we should see a vary small flow rate but this go faster if we blip throttle. A garage can check for cylinder gas leaks using chemicals in coolant that react to combustion gas presence but this is normally only a main dealer. Flow rate. Is possible culprit an for fans? Have we checked fans kick in? A garage can also check coolant flow etc sounds a though you have carried out all DIY checks and are at a loss. Time to place in in hands of a mechanic. Will not eb cheap but will get a fix.

You can't be positive that the head gasket or a cracked cylinder head is not the problem until you have a mechanic do a chemical test called a "Block Test".
After driving and the temp, gauge going up do you have any air bubbles coming out of the radiator neck with the motor running and radiator cap off?
Very small and numerous bubbles that don't purge and stop would indicate the head gasket is leaking.
A full blown head gasket will cause a geyser of water to come out of the radiator neck.

"I'm positive that it isn't a head gasket problem because I have no coolant in my oil"

This is faulty logic! A leaking head gasket doesn't always leak coolant into the inside of the engine, where it ends up in the oil pan.

Sometimes it leaks coolant into a cylinder, where it is burned and disappears without a trace. Sometimes it appears as white smoke (steam) coming out of the exhaust pipe.

Sometimes compression/combustion pressure from a cylinder leaks into the cooling system and overpressurizes the cooling system, which pushes coolant out of the cooling system into the coolant reservoir. If that fills up, the reservoir vent dumps coolant onto the ground.

What might appear as overheating is actually this happening.

When an engine is first overheated, it can warp an aluminum cylinder head, which then unevenly clamps the cylinder head gasket to the engine block. Then the cylinder head gasket leaks. It's not the gasket that's the problem. It's the warped aluminum cylinder head!

Throw your thermostat away

I would start with the thermostat because that's the cheapest, easiest thing to fix. It could be the water pump too, but why would that take 30 minutes of driving to develop a problem? I had a problem with my water pump too, but it leaked like crazy, even though the car never overheated (unless the coolant level got too low).

If you have an electric fan there could be a bad connection, or loose. Or is there something stuck in the front of the radiator, You seem to be having a air flow problem here. A friend of mine had the same problem, her X had put a black piece of cardboard in front of her radiator: once I frond that and removed it it was fine.

Sounds like your head gasket is about to blow