Help please!

Okay, so sometimes, only sometimes after I have sex my period will skip for a various number of months. Last year it skipped for almost 10 months in a row. I never got checked out or anything because I read some other stuff online about how I could be I guess not fully developed, but I’m 17. Back in June I had sex and then it skipped for two months again, and my periods are usually really really heavy, but this time it was light. Advice or suggestions on what I should do?