I would also suggest that you consult a doctor. If you get these sores regularly and they cannot be absolutely attributed to a 'mechanical' cause (biting your lips in your sleep) then there is something going on that is causing them. That cause may be something fairly benign "oh you're just prone to cold sores" or something a bit more insidious (secondary infection, vitamin deficiancy, systemic problem). If it's the latter, then you definitely want to know about it and have it treated if possible.

If it's just a chronic, not too serious problem, the doctor may at least be able to provide some topical treatment that may not be available over the counter, that will help clear things up.