vegetarian with under active thyroid

:mad:
I'm fast approaching 60, used to be really active (surfing, running & cycling) then a few years ago ill health hit me 24/7, last year I was doing triathlon training to try & get toned up, but I lost no weight or even toned up but I've been since advised by my Doctor to only do light exercise, I suffer from an under active thyroid and only have 50% mobility in both my arms, it doesn't stop me from mowing the lawn, digging down my allotment or cycling, but my weight has almost doubled in 5 years and I find it quite emotional & stressful, so if there are any others out there who have an under active thyroid, need to cut down 10 dress sizes and baffled as a vegetarian that you can't eat cabbage, cauliflower, brussels & soya based products as it's not good for under active thyroid - please advise, I don't smoke, drink alcohol & never take diet aids, the only medication I take is for my thyroid & seriously (morbidly obese level) high blood pressure.