am I pregnant

So I got an IUD in June of 2016 and my periods have never been irregular with it. But 2 months ago I had one and then 2 weeks later I had another. But now my period is 21 days late. I've taken 3 of the 88 cent pregnancy test and they've came back negative. I've had really bad mood swings, frequent urination, cramps, headaches, fatigue, and some vomiting in the morning. I'm really confused and don't know what to do! Help!!