2003 Toyota Camry engine coolant temperature gauge slow to reach middle level

Hi,

I've recently noticed that the temperature gauge on my camry suddenly
became very slow to reach the middle of the gauge. Even then it hasn't been
completely reaching the middle, just a little below. I'm not sure if it's a coolant
problem or a thermostat being loose problem. I recently was also having
problems with my air conditioner not working well. The A/C light would blink
and hot air would blow out. But I ended up fixing that by replacing a fuse as
one of the ac parts was not spinning (can't recall the exact names of the parts).
Not sure if that is related.

If anyone does know, what could be the problem? Any answer is greatly
appreciated, thanks.