I have a similar problem as you. I get spotting after sex and it goes on for a few days after. I also have an underactive thyroid, and this condition can cause problems down below eg. it can make your vagina dry which can cause a bit of injury during sex which makes it bleed a bit.
I've only started thyroid treatment, so I'm hoping this won't be a problem for me for much longer once my thyroid levels even out. It's amazing how many problems are caused by an underactive thyroid gland. I've got joint pains, fatigue, my hair falls out....the list goes on! But once the thyroid is treated properly symptoms like these shoud disappear.
You mentioned you have a lot of gas - look in to the posibilty of candida. Thyroid and candida can occur together. Candida causes fatigue, bloating, gas, brain fog etc. Search the symptoms on the web and there's a forum on curezone for it too. Also have a look at adrenal fatigue, which causes fatigue and if you have it, with a thyroid condition, the thyroid won't get better until the adrenal glands are treated. There is a forum on curezone for adrenal fatigue too.