I Had Sex For The First Time With My Gf

I had sex for the first time with my gf and everythng was fine but second time she sat on my dick and i felt pain from that day i am facing issues. After 7-8 days my pennis starts itching and when i see it, it would be full of white thick liquid and its smell is different from the normal smell of penis or semen. I am scared of some infection or any injury. This never happened before but after she sat on my dick(trying cowboy position) i am getting this itchy white liquid problm. Please guide me !