Is it possible to have a d&c for miscarriage and find tissue in there that's been there for a while. after the d&c i feel better than ever before ?

Tissue: Are you having less cramping now after the D&C than with your regular cycle? It's not likely that any tissue there before was removed but that removing the pregnancy tissue makes the lining now thin and you are responding to that with less cramping and pain. With your next cycle, these symptoms may return as your body expels the tissue that builds up during the cycle.

Possible: After a D&C it is possible to have retained products of conception. However, given you are improved, it is unlikely. Be concerned if you have increased pain, fevers or a foul smelling discharge.