Doses of Methyl-cobalamin (not cyano-cobalamin) in the range of 2000mcg-5000mcg per day will help with the lethargy/weakness - no matter what your test scores are
(I would be conservative and say below 600 is sub-normal and needs bolstering)

If it is PN (the skin biopsies will confirm small fiber, that the EMG won't catch) weakness and inability to get motivated can be s/e.

Your age is on the young side for most PN onset- but inherited,
or autonomic causes should be ruled out first.

The dry eyes could be a sx of Sirojens (sp?) syndrome,
& you might want to look in that direction.

As far as the ED, you might want to peek in on the Sexual Dysfunctions forum, here - and see what they have to say.
Usually, with PN, ED is a s/e of meds such as Neurontin/Gabapentin & that genre of medication- rather than the PN itself, but there are such varied sx with this condition that its difficult to rule anything out.

ED is not very common without a medication being in the way, but stress is a huge factor in PN flares-and stress can be the underlying cause for the ED episodes..