Why do i worry so much?

I always make the worse out of all situations...mainly ones that concern my health and they overcome my thinking and daily life. Within the past few months I probably thought ive had about 30 different diseases/conditions....etc..I had foliculitis-thought it was skin cancer...sore throat-thought it was throat cancer...bronchitis/wheezing-thought it was lung cancer...headache-thought it was brain cancer or a stroke...heartburn-thought it was a heart attack..pain in my calf-thought it was a blood clot... pain/bump-thought it was cancer (had it checked, nope it was normal tissue)the list goes on..and id like to say that it completely overcomes my mind and thinking..when i worry about it its an all day thing, i try to cover it up the best i can but my husband knows my issue. Like right now...I keep getting these painful twinges on my head like once in a while maybe once or twice every few days and im terribly scared i could be having a stroke or a brain tumor...and then i get some other symptoms that coincide with the main symptom and these thoughts litterally break me down into tears and scare me...i have no idea why i do this to myself, i even look up symptoms and either have them already or will get them at some point..i can never decipher whether they are real symptoms or if i am making them up....please tell me whats wrong. my dr told me to try paxil...OMG i was up all night, it was the most horrible rdug iver ever had...by the way im 24 with 2 kids...i do take a water pill to stabilize my blood pressure, working on losing weight (from having kids) i dont drink/smoke.....never have