I have been on birth control for about 6 months, and my period has always been extremely regular. However, last month I was on amoxicillin for about 10 days, one of those days I forgot to use a back-up method. I did have bleeding after this happened, around the normal time I would have my period, however, it was much lighter (but heavier than just spotting) and it only lasted 3-4 days instead of the usual 6-7 days. I am now due for my next period next week. I have been having a lot of symptoms, especially nausea and vomitting, and tender swollen breasts. But I have taken two tests, they both came out negative. Could I be pregnant, or is it something else?