Use the caffine BEFORE you start coming down. I've found caffine can't bring you back from sleepiness, but it will sustain whatever level of conscienceness you have going for you. Smoking again also keeps me going. Try and smoke more sativa that will help. Also it may just be a mental thing. You have got yourself in a routine where you smoke and then go to sleep. Try a wake and bake, not all the time, but once in a while, and it will keep you from falling into the mental pattern that smoking = sleep. Also like someone else said, get out and do stuff. Smoking makes you kinda lazy, but fight it, hackey sacking and frisbee are two awsome stoned activities, that you won't get shit for if you are stoned.