Sexually Active. Feeling Nausea And Abdominal Pain After Periods. History Of Appendectomy. What's Going On?

Hi i am 22 years old and am sexually active. I had my period about 5 days earlier than when I was suppose to start. I started around 7:30 pm on july 2nd and my period was gone by the time I woke up on the 4th. It was a brownish color towards the end of my period but I thought nothing of it. Now July 10 and for the last few days I wake up in severe pain in my lower abdomen and feel nauseous especially after I eat. I haven t felt this way ever but I have had a appendectomy about 4 years ago and also I had another stomach surgery on my pyloric sphincter when I was 6 weeks old. I have no idea what is going on.