I have not had my period in the last 3 months and the last time I had sex was 4 months ago and I took a test but it said I was not can someone please help me and tell me what could be wrong with me

Have you talked with your dr yet? We can all take guesses on here trying to figure out what's wrong with you but only your dr will truly be able to make any sort of diagnosis.

There are 100's of reasons many minor, some not. And your home test could be wrong even. So why not merely go to a clinic, dr or health department