From your questions, it would seem that you think you could be pregnant. You should find a planned parenthood and get tested. Or you could go to a dollar store and try one of their pregnancy tests. If you ovulate while you are bleeding, then yes, you could get pregnant. You should assume any unprotected sex could lead to pregnancy.
There are certain times when a women is more fertile but you can get pregnant at anytime. If your not using some form of birth control then chances are you will get pregnant.
i hear if u have a sex on period, it harder for u to get preg. is that true or fasle
There isn't any way to tell without testing. Those symptoms could possibly be std, or could be something else like stress causing your body to react this way. You should talk to a gynecologist about your problems.
if i had unprotect sex would that be some kind std
Probably not. But if you have had unprotected sex it is wise to test. it is also wise to see a Dr.