I don't know this hospital, but it sounds quite typical for UK A&E departments.
I've only been in a couple of times - once I was admitted, but the other time I was getting heart palpitations (never did find out why). I'd never had palpitations like that before and my health wasn't the best so I went. They did do an EKG (I think that's what it's called) extremely quickly, but because it showed I wasn't having a heart attack, they sent me home again right afterwards. This didn't seem a problem to me - they'd made sure I wasn't in an emergency situation, so there wasn't anything else they could do other than tell me to follow up with my GP as an outpatient.
They really are only interested in dealing with immediate emergencies in A&E. If you were conscious, up and walking around, and there was nothing sinister in your blood tests, etc. then other than give you things like pain relief - fluids in your case - if you need it, it doesn't sound like they were particularly wrong in how they treated you. ('Though of course I don't know the details, and if they were dismissive in their attitude or anything like that then they would be at fault). I've accompanied others to A&E and seen them be assessed, told it's not an emergency, and sent home to follow up as an outpatient.
Waiting times depend on which patients are needed to be seen most urgently, so again, if you're conscious and not bleeding to death that's unfortunately just the way it is.
Telling you to continue your medication is important with prednisone, even if you are getting side effects, it's more dangerous to suddenly stop.
That said, they shouldn't have made you feel bad for coming to the hospital - it is part of the A&E's role to assess every patient and judge whether they are an emergency or not - it's not wrong to go to A&E if you're having scary symptoms, even if they turn out not to warrant emergency treatment. The staff should reassure you about that and should never make you feel like you shouldn't have bothered coming in.
You should definitely see a doctor as an outpatient to get the side effects under control or to see if these meds aren't right for you - and perhaps it may be something other than the meds causing the symptoms? It's always a possibility, though it does sound like it's connected to the meds for you since you're not had these symptoms before.
Sorry you had such a bad time and I hope you get things sorted soon.