Please help my confusion !!

Lately ever since I've been on birth control (3 weeks now) I've become overly emotional, I used to get really bad headaches the first week but now I'm very tired all the time even when I wake up in the morning it takes me a good 20 minutes to get out of bed because I'm tired and throughout the day I'm constantly yawning the ending of the 2nd week on birth control going on the 3rd I've been having unprotected sex with my fiancé I don't think I'm pregnant because I took a pregnancy test and it came out negative I don't get my period yet so I don't think that's anything to be worried about plus I'm on birth control so can someone please tell me what's wrong with me ? Is this another birth control symptom ? Or an early pregnancy symptom ? Once again I really highly doubt I'm pregnant