Not to sure what to think? SOS

My boyfriend and I have been trying to conceive , this month a little more then most . My period isn't due for another two weeks. For the past few days almost a week right below my belly button has been killing me ( really bad cramping ) I feel so nauseous all the time. But nothing ever comes up, today my boobs and chest started to hurt ( I haven't done anything differently then what I normally do every other day) . My nipples have been sensitve for a good week now. Normally I feel nauseous and cramps before my period , a few days before. But never two weeks early . I've taken a pregnancy test, and it's negative . I'm trying not to get my hopes up. But I'm not to sure what's going on. Any suggestions ladies ?:) I'm very new to this site! Thanks in advanced!!