Have a look at https://www.mstrust.org.uk/about-ms/ms-symptoms/managing-relapses This should clarify for you if indeed what you are experiencing is a relapse.
You’re right that the standard treatment for a relapse is oral steroids (Prednisolone is the most common). You should be able to get a prescription from your GP, so long as they are happy to prescribe them. Some GPs are unfamiliar with the high dose needed (500mg for 5 days), so it helps for your MS nurse to be aware of your relapse, and if necessary to advise the GP.
Because an MS relapse of the kind you’re describing isn’t an emergency, you might find that A&E aren’t too keen on prescribing the steroids; although they might, if you are desperate, give them a go. Obviously if the relapse was impinging on your mobility or very severe, then A&E might be the best place.
Don’t forget that sometimes there’s an underlying cause for MS symptoms to appear like a relapse. For example an infection. So you should always have your urine checked for UTI before taking steroids (my GPs are happy to prescribe high dose steroids but are very bad at checking for infections before giving them). If you’ve ever had steroids alongside an infection, you’ll know why you need infection ruled out first. (I had a nasty cold that gave me hives so badly that my eyes closed and I couldn’t see. The only treatment for the hives was high dose steroids, but the cold went utterly bananas as a result.)
If your relapse is sensory rather than motor, I’d be tempted to wait until Monday, get into your GP ASAP and tell your MS nurse as well so the relapse is recorded.
If your walking is being badly affected, you could wait until the morning and then try A&E. You couldn’t take the steroids in the evening anyway, so there would be no point going tonight - unless you weren’t expecting to sleep tonight!!
Best of luck. Hopefully the relapse will soon be gone. Remember to tell your MS nurse or neurologist so the relapse is recorded on your clinical notes.