I have every sympathy with your predicament, but unfortunately, you ask questions that mostly cannot be answered here.
Yes, you could have MS, for the simple reason that anybody can. But if you did, it would most likely be complete coincidence. MS certainly does NOT cause outbreaks of anything resembling genital herpes (i.e. cannot have been the cause of your original problem). Also, although there have been many theories and a few scares over the years, I don’t believe MS has ever been conclusively linked to any drug (or food, or activity, or power lines, or any of it). So even if you have been given a “wrong drug” for years, for a condition you never had, it wouldn’t trigger MS. Whether it’s capable of triggering other neurological problems, I’ve no idea. A very quick (not exhaustive) Google suggested Acyclovir’s only link with MS is that it’s been proposed as a treatment, but not a cause.
As to whether you have any chance of successful legal action, you’d need to see a solicitor about that. Very broadly, it would depend what harm you have suffered - i.e. is it provable that taking the drug for years really damaged you in the way you suspect it might? If not, then you probably don’t have a case, or it would be limited to the emotional and practical consequences of thinking you had an STI when you didn’t (which are still serious, but not in the same league as claiming you’d effectively been poisoned). You’d also need to show your original diagnosis was negligent. Not everything wrong is always negligent. If it seemed like a perfectly reasonable diagnosis at the time, in the light of all the evidence available, and the state of medical knowledge at that time, it might not have been negligent. Something can be mistaken, but still not negligent, if you see what I mean. I.e. if it was a reasonable diagnosis to reach, but only hindsight has shown it to be wrong, there’s unlikely to have been negligence. Doctors aren’t negligent just for failing to foresee that time, and perhaps advances in technology, would prove them wrong. Unless you can show they could and should have been able to tell at the time it wasn’t herpes, you probably don’t have a case.
I guess the first priority - for your health, as well as legally - is to establish what really is wrong with you. Then you can get that treated and look into whether there’s any possibility it was connected to the drug you’ve been on, or possibly failure to get the drug you should have had, if there’s been negligent misdiagnosis from the start.
I’m wondering if you have had some kind of auto-immune thing going on (not MS), that causes rashes, and perhaps the more recent stuff too. It’s just a wild guess though, as I don’t know much about auto-immune conditions other than MS, but I do know a few can cause both rashes AND neuro stuff.