std or just irritation?!

Okay, I kinda started hooking up with an ex of mine (we broke up 3 years ago) . He came back into my life the end of April and like 2 weeks ago we started having sex .. okay everything went well and stuff until today .. since yesterday I've been feeling some sort of discomfort on my vagina lips .. like they felt slightly swollen for no reason .. it usually happens to me depending on the underwear I'm wearing or my pad whenever I'm on my period, so far I've been spotting bc I'm now getting off my period but when I go check down there and open my vagina lips,,,there are red spots in the opening area and almost by the clit area!!! And it sort of burns like a rash or like an underwear burn (like if something brushed against it and irritated it)!
I'm freaking out right now and I told him "I swear if you have something I'll kill you" and he didn't blow up my phone or anything, he was like "okay get checked , I mean I shouldn't have anything "
We spoke about stds before and getting tested recently and we both said our results were negative so ok.. idk,, I'm thinking the worse right now bc I'm scared that he might have given the me something  because I explored in and all around his penis for signs of herpes or anything and he didn't have anything that gave me the doubt.. he's an RN too so I'm freaking out in a way but I'm sure he always gets tested.. 
Any thoughts??