I thought i was getting better?

I have thyroid issues due to living a sedentary lifestyle and barely leaving my computer desk. I tried eating only healthy foods but it didn't work. i figured out i had this issue because i wasnt moving enough and not exercising the way i should. So about a week ago i started doing high intensity exercising. Like two days ago things were looking up, i was feeling alot better then suddenly the next day i felt like crap again and since then i've been mostly feeling like crap still. I didn't change anything, just stuck to my new exercising routine. It's very disheartening and i feel like just giving up at this stage.