It might be die-off due to Threelac, try reducing threelac intakes. This treatment is all but a race. With any supplement you take, learn to start taking 1/10 of the dose and SLOWLY increase to the point where you get die off, then reduce a bit.
This being said there are quite few issues involve in your post.
1- there is a FANTASTIC shampoo on the market: Nizoral, it kills candida. It is normal to have candida on your scalp.... I mean it is a standard issue we all share.
2- I use Nizoral, but if - like you - I also had thyroid issues, I would use coconut oil - as a supplement (use it to cook or else on your pancakes: basically like you would use butter) and also on your skin. Put the coconut oil all over your scalp and but a shower cap on for 15 min. to half an hour before you wash your hair (with any shampoo.... like Nizoral, coconut oil is an antifungal). This will help a great deal.