Im a 21yr old lesbian, my gf of 5yrs is23, we've always had constant sex, lately she makes excuses&seems annoyed when i want to make love, is it normal?

Time for a talk: All relationships go through up and down periods. These can be affected by seasonal events, work, personal stress, etc. and long term relationships work through them. Communication is the one issue that either binds or breaks a couple. When intimacy routines change it often signals a person with some form of inner turmoil. If you can get a discussion going,the issues may emerge.