Very concerned someone please help. Little tmi!!! 10 pts for best answer.?

I think i might have a bacterial infection. Im 25 weeks pregnant and last night i saw yellow discharge on my underwear and it kinda burns when i go to the bathroom, and when im just relaxing i will feel it burn and get irritating feeling. I did notice its starting to have a smell to it (gross i know im sorry). I'm not so sure how i would have gotten it since i haven't had sex for 25 weeks and i dont shove anything up there either. I do take a lot of baths (there my favorite). I dont wear thongs, i always where underwear and i change them a lot. And i been washing the same way i have been since i got pregnant and before that to. So what do you think? My next doctors appointment is July 6th. Is it okay to wait or should i make an extra appointment for Monday? Someone please help. She is moving just fine, but i wanna get this figured out now. The yellow discharge only came up last night, but the burning has been gradually working its way up for a week or so. This is my first baby and i told my sister about it who is also pregnant and shes due soon but she told me not to worry all the time she told me it was okay. But now im worried because i read that bacterial infections can cause preterm labor and i really cant have that. So someone please help me, Thanks!!!!!