Actually, I'd say it's normal to see some undigested food in there. Certainly not a lot of it, but a few pieces of foliage here and there doesn't necessarily mean there's a major problem.
Over-active thyroid can definitely cause a lot of problems. Your thyroid controls pretty much everything in your body in some way, so when it goes nutty, so does the rest of you. I was diagnosed with autoimmune hyperthyroidism early this year and it really messed me up. Now I'm on medication for it and my thyroid function is normal. It's pretty easy to control with meds or radioactive iodine if you choose to have that. But first you just need to get your thyroid levels - TSH and free T4 - checked.