I don't think you need a drug, you need a lot of therapy to deal with the loss of your son. It sounds like you never got over it emotionally, and have projected his path onto yourself. This is something therapy can actually help (this is a joke for my fellow anxiety sufferers), but medication will just cover up the symptoms. This is something you need to face. At least that's how I see it from the little you posted.
I'm so sorry for you're loss. its natural to have fears, but you need to keep your self healthy so you don't get sick, try to do thinks that prevent cancer. i had thyroid cancer almost 2 years ago, im having a recheck,and felling anxious about it. but the best way to fight ist is to b positive. so when you fell this way remind you're self that this is just anxiety. question the felling like. " well if i have cancer wouldn't i feel this" challenge the thought.
good luck!