Ugh -- my condolences. I had a pretty bad case as an adult (I was 27). I was sick for about 3 weeks (the itchiness + the fatigue).
I only have 1 or two tiny scars, hardly noticeable, but they are both places where the scabs came off early, so DON'T SCRATCH! (and always pat dry after a shower/bath.)
Things that help:
-- make sure your doctor prescribes acyclovir (which will damp down the viral replication)
-- mine also put me on a powerful antihistamine that also has anti-anxiety effects (Atarax/hydroxyzine) -- it definitely helped when the itching got excruciating
-- oatmeal baths (Aveeno is good)
-- Calamine lotion
-- light sheets on your bed
You'll be contagious for a while (your doctor will know how long), so plan on staying home
Didn't have any complications, luckily: that was the intent of the acyclovir, so I guess it worked.
I would guess you'll be out of the gym for 3-4 weeks -- I started swimming again after about 3 weeks, but it definitely took some time to get my energy back.
P.S. This is against all the advice you'll get, but it helped me: when the itching got to be too much, I'd take a really hot shower, with high pressure -- not enough to dislodge any of the scabs, but it felt
like I was able to itch. Only for acute emergencies, though -- it can raise your general itchiness, though it helped me for the most aggravating ones.