At zero but desperate for more

Some backstory: I'm 29F, overweight, and have PMOS and IIH (idiopathic intercranial hypertension).

I have no built muscle. Like. None. Lifting 15lbs is rough. I'm like a damn spaghetti noodle. My core is weak. Anything that puts too much strain on my shoulders/head or sends a "rush" to my head is a hard no. How else can I build muscle?? I tried following a YouTube video for dumbbells with 8lb weights and I had a pressure headache for 3 days after. I'm at a loss. I want to build muscle and get stronger so badly but I feel like this stupid condition is setting me back.

Also yes I am being treated for it and day-to-day it is managed! I don't get headaches anymore usually. Only when I do things out of my norm or put too much strain/pressure up to my head does it act up!

I just need tips on other ways to do this, what workouts will help me achieve my goals? I really would like my arms to get stronger as well as my core.