Help/advice

So for the past couple of weeks I have been having mild abdominal cramps/pains as well as lower back pains, but it wasn't until Sunday that the cramps have gotten slightly worse, not bad enough to worry about but just more uncomfortable. Also my lower abdomen hurts if I have anything pressing on it, so like my seatbelt or jeans or other tight pants, even just wearing leggings hurts. Af is due between now and tomorrow so far there's been nothing, I've taken a few pregnancy tests but they have all come back negative, is there any other reason I would get these symptoms???