Lip annoyances.

Hey everyone. This is probably something that some deal with and it's finally getting to get to me. I'm a graduate student on horn right now and I have had a history of lip problems since my freshman year. First it was nerve pain for my 4 years as an undergrad and I finally figured out how to avoid the pain which is great. However there is a rare moment when I can't play any notes at all. When it happens I have to work to build it up for weeks if not months. So I'm wondering if others deal with this and how they cope with it. It's really discouraging and it happens when things are going so well on the horn. Any other stories about this are welcome. Thanks.