Re: Is it an STD, or just a yeast infection?
It does sound like you just have a yeast infection with a possible urinary tract infection. Diflucan is a great medication for yeast infections; it's a one-time tablet that should clear it all up. For your urinary tract infection, however, proper medication needs to be taken as these will not clear up on their own. The doctor can perform a simple urine test where they will check the pH balance - or in some cases may just give you a perscription for it anyways.
I would suggest going to doctor and while you bring up your concerns of a yeast infection and urinary tract infection, also request a general STD swab - for chlmaydia and gonorreah. These swabs are most effective when performed at least 2 weeks after sexual intercourse as you will have given any possible diseases enough time to establish themselves in your system.
Over the counter treatments for yeast infections, such as Monistat, can be helpful, but sometimes women may tend to go for the 1- or 3-day treatments and they may not clear it all up. The 7-day treatments are better - but if given the option of the Diflucan pill (which is only available via perscription), I'd go for that.
To help prevent these infections from coming back, get on a routine of taking Lactobacillus acidophillus. These tablets will balance out the good bacteria in both your digestive system as well as your urogenital system.