nausea, headaches, exhaustion, peeing loads.. but on birth c

I am sexually active with my boyf. I am on the birth control pill and didnt miss any last month. I had my period last week when I finished my pack, but felt different to usual. I may just be being silly but the cramps felt different, just wierd, can't really explain it. To be on the safe side I took a pregnancy test during my period and it came out negative. So all this would surely suggest that I can't be pregnant.. BUT I have been feeling nauseous on and off for nearly two weeks. I have also been getting stabbing pains in my head, behind my eyes mainly and then this morning i woke up with a dull ache which didnt die down for an hour of so after taking pain killers. I been feeling really tired recently and find myself having to go to bed really early. The problem with that however is that i end up waking up in the night or really early in the morning having to pee. In fact strangely, as soon as i get into bed I seem to need to pee every half an hour or so til i fall asleep.. (ok, so i mightjust be wierd). I've been having major mood swings as well and had sore breasts (but only for a day or so) last week. Any ideas what could be causing all this??? Coz surely not missing any pills, having a period AND havin a negative test result would rule out pregnancy! I just feel really strange.. Thanks :-)