help with radiater.

Ok, So, thursday afternoon my car over heated coming back from school. I had been keeping my eye on the temp gauge since we have been having 100+ degree weathers here in So Cal. So, while on my way home, my temp gauge didnt even gradually rise, it just jumped to a little over normal tempature, which makes me question if the car was a little hot before hand, however , that isnt my problem anymore, cause i do plan on ordering a new temp and oil gauge just to have a more accurate reading since my car is getting up there in milage. SO, my problem is, i flushed out my fluid, the car was a little warm when i did it, so, by the end of the night, i ended up topping it off, and now tonight, my rediator reservoir was low again. Like really low. Im getting worried about this because im fearing the worst, which is a head gasket leak, but tonight, when i checked my oil, everything seemed fine, i didnt spot water in it. and i havent noticed any leaks in my radiator whats so ever. Someone told me i might have a hot leak, but i dont think that either. So, my question is, where the hell is it going??? is it possible its evaporating while im at school and driving with these heat conditions???
 
No, when you flush it and it's empty, you have to start it and fill it many times. Then start it and get it warm until the fan comes on and fill it again. Then again - then should be fine. Trust me, have to do this everytime a 4.6 is dug into. I've been dealing with a heater core fritz and a pin hole leak (hot leak that wont really drip ever, just wont hold 16psi) and an almost overheat as of late. So any q's you can pm me or call me if you still have my #.