Stupid but serious question

So if you are getting your monthly period, that means your not pregnant right? I had sex with condom and its been 3 months and i am getting my period so that means im not pregnant right?! The reason im asking is because i feel like my belly is a tad bigger or something, i weigh like 106 so am i just getting fat there? Ive always been skinny ... what do you all think??? Sorry but i just need to know. Thanks girls , and dont worry i dont plan on having sex agian until years from now...