I often have unexplained bruises, and other than one or two that I can remember that were particularly large, I don't really give it much thought. And I also have pretty sensitive skin, so rashes aren't all that uncommon either. As for the burn looking thing, impetigo can resemble a cigarette burn, so is that a possibility? Also, I recently had a basal cell carcinoma removed (no real big deal), and it was a scaly red patch, that could have resembled a healing burn...
I tend to do exactly what you are doing with health related things, though... I immediately go to certain death as my prognosis for everything... I had a little lump on my ear, and I know a lady that died from a cancer that developed from a lump on her ear... so you can imagine. I literally thought I was dead, and while I was waiting for the biopsy results, I nearly lost my mind. And it was nothing. Nothing.
I can't tell you not to worry because I do too... but with the things you described, coupled with your MD husband's apparent lack of alarm, I think you should take a few deep breaths, maybe a long, hot bath, drink some tea, and hug your kids. I think you're going to be ok. Hang in there.