Check your position of your hands, forearms, fingers, shoulders, neck. If all OK, just get into the rythm and get going. Relax once in while, take a break, listen to some music, and get going again. Try playing to songs you know and like. Get tabs or chords from books, and just go at it.
Metronomes are boring but nessecary.
Try playing with some of the jamtracks here - they'll help you get into rythms and sound a darn lot better than metronomes.