whats going on?

Last week i got a negative pregnancy test, even though i was a week late with unreal cranps. On monday (cd38) i came on my period like a usual period, and this was the same tuesday. On Wednesday i didn't bleed, and thursday and friday (today) i only spotted once. Normally my periods are really heavy and last 6 days. Recently get the odd sharp pains in my boobs and they kinda ache sometimes, and two weeks ago i was extreamely nauseous and fatigued.