You probably lost the musclemass because of the quick change of diet leading up to the Ayahuasca. Certainly, it's still possible to stay in good shape with a high protein veggie diet, but otherwise, yes, the muscle will fly off, especially if you're not doing weight preserving exercise and not used to the new diet. Eating meat isn't essential, but getting a veggie diet 'right' is very important. It's too easy to 'fill up' on fibre and starch, but there's no protein in that.
Personally i would say either work at the veggie diet, or maybe return to healthier proteins and of course some muscle bulking basic strength training, starting with light weights. If you get no luck, see your doctor, it may be something else.
"Eat your vegetables and do as you're told, or you won't be going to the funfair!"