Thinking of stopping azathioprine

So I am taking azathioprine 100mg a day and Humira once a week. I have been doing very well except for the occasional migraine after Humira and some minor problems. I have to see my GI next tuesday and I was thinking of stopping azathioprine. I had stopped it before because he had told me to because it came out in my labs that I had increased liver function. So stopped it and was taking Humira once every 10 days. Last time I went to see him I told him I wasn't doing well at all and he upped the Humira to once a week and tacked on the azathioprine again for 100mg a day. Now that I am feeling a lot better I was wondering if maybe it's just because the Humira dosage was increased. But he had said that the azathioprine was to prevent Humira from becoming resistant. Is that true? How does that work if it is?