Hello,
I've been having A LOT of yellowish discharge since I had sex for the first time 3 days ago (I've been wearing panty liners and changing them 4-5ish times a day). No itching or smell at all. It was (stupidly) unprotected sex, but I just started the pill (on my 3rd week, so condoms aren't technichally necessary). Sex hurt a bit and I was sore the next day, but I think that was just because my boyfriend is well endowed. Since I'm on my 3rd week I'll be getting my period next week. My last period (the one I started my pills after) started with similar discharge a week before also, but not as much. I didn't have my period for 2 months before said period - so it isn't enough to establish a pattern, but I don't know if the sex and the discharge are related, or if it just so happened that it fell the day before I started my weird discharge thing. Sorry for the long question and run on sentences, but any input would help!

It could very well be a STD since your sex wasn't protected.

Oh, and condoms are still necessary if you aren't ready to be a mother. I used condoms AND the pill and got pregnant not just once, but twice.

Yes, I would see your dr. as soon as possible. There is a very good chance it is an STD.
Always good to wear condoms, even if on pill, due to STD's as well.