It could be yeast infection, it doesn't have to go really bad straight away.
It could also be just an irritation cause you had sex so many times in such a short space of time.
From my experiences I can say that you can get yeast infection like that, with loads of sex if you're not use to having it that often. Just drink loads of milk, yoghurts. You can wash yourself with probiotic yoghurt (rinse with water afterwards). Don't use shower gel or anything that has perfume in it, that irritates vagina even more.
Don't wear tight clothes, preferably no pants at all or just cotton underwear.