Nicola, to give meds when they're breastfed depends on the meds. If they're okay on their own, like in a syringe (Zantac is like that and I think Gaviscon), then you just give it to them. Things like prevacid or losec are often mixed with something, like food - I know with the prevacid, I couldn't do it with the breastmilk, because they don't dissolve. But Sam was over 6 months, so we did pears....
With regards to thrush, are you having any symptoms and did your GP talk about treating you at the same time? Usually with thrush, it's recommended to do both at once, so you don't pass it back and forth....
