Confused

Hi
Hoping someone can help me as I am really confused with working tax credits.

I know I have posted about this before but still really confused. I work 38hrs a week and earn around 20,000 each year. I also get low rate care of dla. My income has reduced this year from 22,000 to 19,900 ( approx figures). My sickness is quite high due to fibromyalgia ( which is why I get dla) so this would put me at a disadvantage of finding a different job. My wage decrease was due to a change with shifts to accommodate my symptoms of fibromyalgia. I am married and my husband is currently claiming income based jsa and looking for work.

I think I qualify for wtc with disability element. Firstly am I correct. Secondly if I worked overtime and earned between £100-200 monthly extra how would this affect the tax credits. I am really confused with the amount for disregard. I only ask as I would like to try and pay for a Holiday in the uk later in year but don't want to get my self in a pickle and end up owing them money because of an overpayment. Would I have to ring them each month with any extra figures.

Any help greatly appreciated.

Woody x