1. "I keep sniffing and blowing my nose" (Sorry, this answer is going to be a little graphic/gross).
This means that the person is probably sick and has mucous coming out of their nose. "sniffing" means to inhale hard through your nose to try to pull the mucous back in. (Note that this is usually spelled "sniffling".) "Blowing your nose" means to exhale hard to try to push the mucous out.
2. "I’ve got athlete’s foot."
Athlete's foot is a kind of fungal infection in your foot that you can get from wet, nonporous surfaces. It's called "Athlete's foot" because the floors of locker rooms that athlete's commonly use are perfect for transmitting the infection, so athlete's commonly get it.