How do you know when a headache is bad enough to go to the hospital?

I have had a severe headache for 48 hours and counting. I spent the past 13 in bed because I couldn’t move. I am up now because I’m thinking of actually going to the hospital. I saw a doctor at a walk in clinic and he said it’s a migraine and prescribed Imitrex, which did not help. This is the worst headache I have ever had. It is a constant pain on one side of my head. I woke up with it a few days ago and it does not go away no matter how much tylenol I take. It keeps me up at night. I have a bunch of other health problems going on right now and I am a cancer survivor, but I never have migraines and I don’t get headaches often. How do you know when it’s time to go to the hospital? I don’t want them to tell me to suck it up.