Car running hot

What is your question?

My car is running hot I replaced the thermostat on the left of the engine it is still running hot. When first driving I can go about 45 mins and it’s fine then runs hot. I refill with water and lasts less than 45 mins no water is being used from the reservoir. Why? We are currently replacing the water pump but the mechanic said the water pump was fine. There is no leak under the car when sitting. It’s like there is no water being put back into the engine. What could be the issue?

What makes this problem better or worse?

Better when first drive of day.

How long has your 2012 Nissan Maxima had this problem?

Weeks