So I Am Kind Of Worried. I Was On Depo-provera

So I am kind of worried. I was on Depo-provera for 2 years then I had my last shot October 2015. In May I got my monthly back and I had it for May and June. I'm not usually sexually active but on the 15th of this month my monthly was due. On the 17th I still haven't received it and I had intercourse with a guy without protection. I still haven't received my monthly yet and my mood swings feel like a roller-coaster. They are constantly going out of whack from one extreme to the next. I have been having period like symptoms but no monthly still. I took a home pregnancy test and it came back negative. Could I possibly be pregnant or could it be something else?