Tea Tree oil,Melaluca..have You used it????

Hey all, Im at my wits end! My P.P. is just under 5 pounds, and every time I apply his Frontline he is sick for a few days! We ( the Vet and I) have tried several atlternatives but they seem to be too harsh or just do not work for any longer than a week! Someone suggested Melaluca..TeaTreeOil!! I heard it was safe and worked realy well at repelling fleas,but I just dont know how to apply it! KNowing that it is an oil, it must have to be diluted to use on pets! Can any one help with some info here!