Vaginal Itching after first time

I had a very small yeast infection, and it seemed to go away on its own. But the other day my boyfriend and I had sex, which was my first time. I knew that pain during your first time was common for most people. But .. I'm gonna say about 45 minutes to an hour had passed (after we finished) my vagina got really irritated. It actually felt exactly like the very first yeast infection I ever had, which was incredibly annoying. I told my mom and she went and bought a generic version of Monistat, which I really don't usually like the generic brands, I've found in the past that it hasn't even completely gotten rid of the yeast infection before. But anyway she got me the 3-day treatment, and I've used 2 days of it so far. Usually when I use Monistat the irritation starts to fade away a great deal even after the first day, but it's hardly changed at all and it's been 2 days of treatment. I know it has to be a yeast infection, because I've had them before and this feels like the first one I had. But it's just being incredibly stubborn and it wont go away. I've been applying the cream throughout the day and the treatments at night before bed, and drying after showers and everything. I've even been using K-Y Jelly occasionally. Could it just be that the treatment I bought is a rip off? I mean, it was about 8 dollars less than the 3-day Monistat treatment so my Mom wanted to get it. But I really haven't seen any results at all. Could I just be irritated from my first time?