I think physical problems can definitely make you feel like a nutcase on an emotional level. Even a mild hormonal imbalance can change your personality dramatically. The check thing, the store thing, nothing seems particularly ocd to me about that. Maybe a tad neurotic with the white out thing, but I would probably worry about a bill for $200 going out in a rainy mailbox. IN fact, I will one up you, I would probably not leave anything in my mailbox important with the flag up. I usually drop it directly at the post office.
I also remember how BIG things seemed when I was younger. Age teaches you one thing, and that is things are often only as important as you give them credence for. Your health IS a biggie, don't misunderstand me, but I remember a girl in high school coming up and telling us she was going home because her pants swished together around her thighs and "oh barf, it made her feel fat and she could diiie' and she was too depressed to stick around for the rest of the day. We laughed a lot about it at the time, but sometimes that is all it takes for some people.
Changing your focus onto what IS good might distract you from obsessing on things. It takes QUITE A BIT of concentration to stay focused on the positive, as some days things seem to just pummel you with the negative. But mostly it is just a decision. If you cannot change the situation, move on immediately to another thought. No point in dwelling on the bad if there is no immediate solution to it. It is easier than you think. Take care of what you can make better and leave a bit in God's hands. Do something that makes you happy. People always forget that is a choice.