Boyfriend of Accusing me of Cheating

My man is currently flipping out because he thinks I cheated on him. Mind you, I've never cheated on this man or really ever gave him a reason to think I was. A couple of weeks ago, he found a pair of underwear in my purse. They were clean underwear and I put them in there bc I didn't have time to change before work (like truly laaate as anything!) so I figured I could just change into my work clothes and a clean pair of undies when I got there. I know maybe it's stupid but whatever, it was totally innocent. So he found them and is like "ur fucking someone blah blah blah". So anyway I told him what happened and he believed me. Now, several weeks later he found a pregnancy test in my car. I recently had a D&C so I wanted to make sure my levels were coming down plus I was having symptoms so I thought I could be pregnant. He found the SAME pair of undies in my purse and for some reason thinks they're different ones than before (he's an idiot) but they're not cuz I never took them out nor put another in. He's seriously trying to break up with me and thinks I cheated on him, won't listen to anything I say. What the f do I do?!