It is a scary time, there’s no way around that. But assuming it is MS (and your neuro seems fairly certain), then starting on a disease modifying drug (DMD) is a positive step.
In the early days of relapsing remitting (RR) MS, you are likely to be healthy and fit for years to come. And it may be that Plegridy works so well that you don’t have any relapses so you’ll be able to just live your life as normal, just with a fortnightly subcutaneous injection. (This means a tiny needle that just goes under the skin.)
Plegridy on average reduces relapses by 30%. This can mean that it works brilliantly and you’re one of the lucky people who has relapses reduced by way more than this. Or you could be unlucky and keep on having relapses. In which case you can switch to a more effective DMD. And there are lots of them available now.
Subcutaneous injections sound a bit scary, but they are much easier than you think. You just go for a fleshy part of you, your thigh, bottom, stomach for eg. Wherever you have a reasonable covering of fat. You’ll get an autoject device so you just point the thing at the skin and press a button. If you get bruised from the autoject, you can swap to just using the needle.
You may find that you have slight fluey type reactions from the drug. You deal with this proactively by taking paracetamol in advance of symptoms.
Have a look at https://www.mstrust.org.uk/a-z/plegridy-peginterferon-beta-1a The MS Trust website is an excellent place to look for information on drugs, symptoms, almost any aspect of MS.
I would expect that a person diagnosed today with RRMS will live without disability for many years.
I know that no one wants to join this club, but welcome to the forum anyway. Feel free to keep asking questions on the Newly Diagnosed forum, or on Everyday Living. There is usually someone who will at least try to help, or who has experienced what you are living through.