You answered your own question by admitting you've been a hypochondriac.
You've been through a rough time. I would suggest (and I know it's hard) that you stay away from the internet for searching symptoms. That would be easier said than done, I'm sure.
You've been to the doctor and have been told everything is okay. Try to trust in those words. Everything is ok. You're ok.
Perhaps the grief of losing your father has really triggered this badly for you. Might I ask if you are on any meds?
If not, would that be something you would consider?
I have OCD/anxiety. Meds have helped me tremendously...until I stopped for a while because I'd been on them for years.
I did well for a while and then everything came back, OCD/anxiety and almost agoraphobia. Every time I start the meds again, I get the side effects and stopped. A few weeks ago, I promised myself that I would stick it out, side effects and all, because I remember how well I did when I was taking them. It's a tough road. But yesterday was the first day that I started to feel the "shift". I started to feel "me" again. Not much obsessing. Not much worrying. Getting out and doing. To think a few days ago I couldn't. Everything looked so dark. Today I have a smile on my face.
I wish this for you, too.
You said "something has to be wrong, right?" yes, it's called anxiety. My advice is, if you aren't on meds, consider giving them a try. If you are on meds, perhaps a dose adjustment or different med will help you. Just my 2 cents. I wish you well!