How to tell if it’s RSV

I have a 6 week baby who I took to the doctors and they told me he just has a cold and told me just to keep an eye on him... what are some RSV Signs? I’m so scared about him getting that.. right now his temp is staying in between 99 and 99.6 and he isn’t coughing during the day only really at night during his sleep, he is sneezing a lot and sounds really congested but nothing comes out when I suck his nose... any advice? First time mom here and I’m so stressed out 😭 and before anyone judges me I have no idea how he got sick, I’ve been so good about keeping people away and making everyone wash their hands I even Lysol the house daily