Difference between pregnent stomach and fatt stomach?

as a women I realize that i gain a lot of weight in my upper arm area and stomach! and then lastly i will gain it at my thighs. I am 112lbsand the last time i had was in may. i had my period in may, june, july, august and sept. now its nov and havent gotten it yet and my stomach looks a little big. im kinda freakin out cause i could be pregnent? and when i turn to the side in the mirror i look pregnent. someone tell me the difference in appearance. thankss ;D