Women some times take a warm-up time to get excited and to have fun.
You may want to try more foreplay.
I would also recommend asking her what she really likes doing while having sex. Does she like oral, clitoral stimulation, G-Spot stimulation, what positions does she like, things like this will solve your issue very fast. She may just need to try a different position or tell you what she really likes.
Ask her to guide you to what she wants, if she wants it harder or faster let her tell you that. You'll enjoy it either way, and she'll get what she wants. Sex has to do a lot with communication and the better you communicate the better sex is and your relationship as a whole.
So ask her whats going on and what she liked in the past, have her guide you to where she enjoys it most. I'm not sure if you know where the G spot is but I linked you a picture. Its on the inside of the vagina 1/2-1in in on the belly button side, its going to feel like a rough patch of skin and you are going to want to massage it. Make sure your not scratching her, that can cause damage. She might really enjoy this and if she feels the need to urinate tell her to because its not urn its ejaculatory fluid. Her vagina will contract and push your hand out and she will orgasm, this can be done multiple times.
