Strained my upper back

I spent time with a very active friend 2 days ago so we did some outdoors activities, one of which was hanging from and climbing a rope which is something I merely tried for a few seconds but that was enough to strain myself. I am very weak and skinny, twig arms...
Yesterday I had almost no pain but the little I had was in my right shoulder mostly, now its at the base of my neck and I might be a bit swollen but it's hard to tell. I could just be stiff but i'm gonna go with swollen since the pain is worse. I dont have a proper pillow right now so that probably hasnt helped and my posture is crap so I already get random neck pains as it is.
I took a painkiller 2 hours ago and now the pain is back again just as badly as before I took it. I strained my lower back 5 years ago so I know strains hurt like hell but I had forgotten just how bad it is the first few days... and my pain tolerance is very low. I have no other symptoms besides pain though, just a bit of stiffness but I can move normally so my range of motion is not limited. I am going to book an appointment with my old physio tomorrow morning but I know from experience that you usually have to wait at least 2 weeks for an appointment... and obviously a strain is not an emergency. I know all it can be is a strain but im an anxious person so im seeing my physio just to have it confirmed and to get the best exercises to relieve the pain. Any advice what I can do for now?? The pain is currently insufferable and I hate taking painkillers but I have to...