Your doctor can make the case for the increased dosing.
I would not worry too much about your arthritis. You've only had 1 subq injection of Stelara (so it's very early) and you only have two joints affected. That is actually a good sign!
Both my girls started out with many more joints affected - the younger one now has arthritis in her SI joints, hips, lumbar spine, knees, heels, ankles, fingers, wrists, elbows, jaw and possibly her cervical spine.
My older daughter has less aggressive arthritis, and she has SI joints, lumbar spine, hips, knees and ankles involved.
It's way too early to tell with Stelara - I wouldn't give up yet. We were told at least 3 months and up to 6 months. I would wait until you've done a few more doses and see what happens. Then if it doesn't work at all, I would consider an anti-TNF.
Since there are so few biologics, you don't want to go through your options too quickly.
The knee injections should help with the swelling and inflammation in your knees while you are waiting. They really worked like magic for both my daughters.
I know Stelara is technically only approved to be given every 8 weeks, but doctors can often play with the frequency/dose.
For example, Humira is normally given biweekly, but we were able to give it weekly and then every 6 days. Simponi is given every 4 weeks - we got it approved for every 2 weeks because my younger daughter's arthritis is so aggressive.
I have also seen on the forum that some people are taking it every 4 or 6 weeks for their Crohn's. With your case it will be harder - because it's your arthritis that is flaring and not the Crohn's. But it may still be possible - it may just take some fighting with insurance.
As for Pred - some people see huge improvements at 10 mg. My girls don't - both really need at least 15 mg Pred or even 20 mg to make a big difference to their arthritis. But everyone is different - there are some people who respond well to 5 mg.
Good luck!