If you had sex for the first time in 3 months last night, you're definitely not pregnant yet and therefore wouldn't be having pregnancy symptoms. Also, pain on your right side isn't usually a pregnancy symptom. ALSO, your period is due next week which means you *probably* ovulated last week which means you couldn't get pregnant now anyway.It could be an ovarian cyst (cyst on your ovary), ovarian torsion (your ovary twists and it cuts off the blood supply for a bit. It's very painful), appendicitis (infection of the appendix), etc.Can you further describe your pain? How bad is it? Is it constant, or does it feel better when you do something (like put pressure on it or lay down)?

Ovarian cyst is a possibility

Ovulation? Appendix? 

Gas? Try moving around