Should you put a comma after "I am fine, thanks." or is it just "I'm fine thanks."?

trying to learn english more and when i wrote him back I used comma after 'fine' and she said it was wrong. o.o she said it dosent need a coma becaue it is a small sentance..that dont make sense to me but who knows. so, do you put a comma before thank? thank you for help. :D