If you don't mind me saying something so direct, you can get thrush from a sweaty penis that's been inside pants all day, because it's little damp corners of the body that give little yeasts a happy home to live in. Washing hands and peens before sex can help prevent itchy girl parts.
That said - if you can get in to see a doctor to confirm the thrush (called a yeast infection in the US by the way), it's a good idea. Just the first time. After that, you know how to identify it, and you can self-treat.
Or if it's hard to get in to see a doctor or takes too long, you can just try a commercial remedy, usually a cream or a waxy thing you insert with a little wand that comes in the package. Sometimes both, the waxy thing plus a cream for the exterior vulva to stop the infernal, infernal
itching. If you can't find anything, a folk remedy is to insert some live-culture yogurt (and/or eat lots of live-culture yogurt). The friendly bacteria and acidity help restore the balance. After all, there's always bacteria and yeast/fungi hanging around in there, it's just that sometimes something gets introduced and things get out of balance. If you have to take antibiotics for some other reason, for example, you may get thrush from that, just because all your normal happy bacteria got killed along with the evil bad ones.
I always keep an extra pack of over-the-counter treatment in the bathroom cabinet just in case.
Bear in mind that if it's a bacteria instead of a yeast that's overgrowing, it'll get worse instead of better when you apply an anti-fungal remedy. But it is way, way more likely to be yeast.