Is there a chance I may be pregnant even if the HPT says not pregnant?

My stomach is hard bellow my belly on, I've been having really bad cramping, nausea, occasional headaches, indigestion, gas and fatigue. I was 3 days late for my period, my cycle is a little irregular. I had a little spotting one day, it ended the next, then came back the following day, then ended the day after. I took 2 home pregnancy tests a week after I had the spotting, but they both showed negative results. Is there a chance that I'm pregnant?