On birth control but still having symptoms

I was 14 days late on my cycle... Which come on time each month.... I went to the hospital to get checked up because I am on an IUD but have been having every sign of pregnancy except morning sickness... After they examined me ....down there.... They said negative and I started the next morning which I thought was weird. Also it wasn't even normal way darker and extremely heavy ... Which never happens... Plus clots.... Can anyone tell me what should I do