Take him to the vet and MAKE them do blood tests etc
I kept taking Charcoal to the vet, he must have seen about five different vets, and they all just said that there was no reason for his (very significant) weight loss.
Like a fool I thought that my gut instinct was wrong and that ALL of those vets COULDNT be wrong.
I just watched him waste away, giving my husband constant earache that something was seriously wrong.
The last week that it all happened Charcoal had dropped from about 1200g to 700g.
I took him back to the vet and for a change they actually checked his back teeth and they needed rasping, which they did that day, without anaestetic.
He seemed fine and cheered up and for a day he seemed to gain a few grams.
Then it all stopped and he went downhill rapidly, he actually lost another 100g in the time between rasping his teeth and him dying!...a matter of around 4 days!)
I took him to the vet that day knowing that it was the end.
The vet said that if he was a bit fatter then they would take bloods etc (oh funny, coulda done that 200-300g ago!) but that he didnt even have muscle mass any more, then they didnt know what else to say.
I said that I did and we put him to sleep, he would have been dead by nightfall anyway, but I didnt know if he was in any discomfort, so we helped him out.
What I am trying to say is...dont hesitate when a big weight loss occurs...take him straight to the vet and dont let them palm you off, force them to do more tests and get it all sorted.
I dont want anyone else to experience what I did for that 6 or so months, when I knew there was more to it, but let the 'professionals' influence me (they have you thinking that youre just a paranoid 'mama/papa') and I will NEVER let it go again, if it happens to one of my other piggies then I will INSIST that they take bloods etc
Good luck with Lenny, it may well be a very simple (and solveable) problem, but dont let it go on as long as I did.
Get your boy sorted and dont take no for an answer!
Good luck
xx Steph xx