Hello, I Am Having A Lot Of Symptoms. I Have

Hello, I am having a lot of symptoms. I have shortness of breath, I feel like my stomach is being ripped from the inside out, as if someone is taking their nails and scratching it over the inside of my belly. I have bloating, my stomach is poked out as if I'm pregnant. I have taken several tests and they say negative, but my period is not due until the 25th. I feel as though I may be pregnant, but I've been pregnant three times and have never, ever experienced these symptoms. I didn't even know i was pregnant until after I missed my period. I also have constipation and tender breasts. I can only sit straight, as laying causes me trouble breathing. Any idea?