Hi, I had problems with thrush on my nipples (and also in my milk ducts - mega ouch). DS didn't seem to have it in his mouth, dut the Dr prescribed Daktarin for him anyway. The Daktarin didn't work for me and neither did the oral medication I was subsequently prescribed, possibly because I have taken it for vaginal thrush a couple of times in the past. Anyway, I did manage to treat it very successfully with natural remedies. Here's what I used.
Good quality disposable breast pads, changed frequently. Cheap ones aren't very breathable and create a warm, moist environment that thrush thrives in. I found Lansinoh to be the best.
After each feed I wiped my nipples with a solution of white vinegar (one tablespoon in a cup of water).
I then applied coconut oil (sometimes known as coconut butter, available in health food shops) which is anti-fungal but also gentle and conditioning for the skin.
I changed my bras daily and soaked them in Milton fluid before washing. Not sure how necessary this is tbh, but lots of websites seemed to recommend it.
I took good quality probiotics and also gave DS probiotics suitable for infants.
If this lot doesn't work then you could try bringing in the big guns, aka gentian violet. It's one of those old-fashioned remedies that treats all sorts of infections. It's not that readily available. Some chemists stock it, otherwise you will have to order it of the Internet. I ordered some, but was pretty much better my the time it arrived. It's very messy, but very effective. To use on yourself, apply to your nipples with a cotton bud after the last evening feed and wear breast pads and an old bra an T shirt to bed to prevent it getting on bedclothes. One or two applications should do it. You can also use it for DS by applying to your nipples directly before a feed (be warned, he will have a purple mouth).
Thrush is notorious for returning so it is important to keep up treatment for a couple of weeks after the symptoms ease. If you find the Daktarin works for you and don't want to bother with all the rest, the one thing I would recommend is coconut oil as a preventative measure. I just use it in the evenings now as it is a nice moisturiser as well as keeping the thrush away.
Hope some of that is helpful. It's a really miserable thing to have, but it does get better.