constipate tortoise

by AShleigh hale
(berkshire )

I have a horsfield tortoise,.about 20 -30 years old. for the last two weeks he has become sluggish and hasn't posed for about two weeks. I've taken him to the vets and he said he is perfectly healthy but Im really worried. i have tried lettuce, bathing and giving him lots of room.to move but still nothing. he also keeps making a hissing noise, then pulling in his head and rubbing it on his arms. i don't know what to do so if anyone can offer me some advice it would be appreciated.

I got him from a rescue centre and he was pretty badly treated. he was kept in a vivarium so had accelerated growth, a majorly overgrown beak and wasn't used to being handled but its all changed now.