Yeast infection????

Since Saturday September 20th, I have been experiencing redness and irritation on my vulva (the lips of my vagina) I thought I was allergic to my lace underwear I was wearing that day but it started to become very itchy so I put a mirror on the floor squatted down to look inside my vagina I saw a lot of milky white discharge so I took a Q-tip and took a little sample it didn't have an odor and it wasn't cottage cheese looking or clumpy it was just smooth and Snow White and also I do not experience a burning sensation when use the bathroom I think I do have a yeast infection? but I'm not positive I had unprotected sex on Thursday September 18th and I am also taking an antibiotic right now called amoxicillin due to me having tonsillitis the week of September 15th I read on that sometimes antibiotics can cause yeast infections and I also made an appt for Monday the 29th to go see a OBGYN I am totally freaking out!!!!! This will be my first time going to see an OB what can I expect?? And what if I have a STD? I'm so scared!!!!!!!!!