Solo?

If you've done Cadwell's Silver and Gold, then grinding and PvP are your best bets. I play multiple characters and when I took one out of storage at VR12 (which was the highest rank last time that character had been played), I went to VR14 in a little over a week in Cyrodiil.

If you change your mind about the solo requirement, find questing groups in Crag. They need help getting completions, which involves things like fighting anomalies and clearing delves, so at least you won't be as bored by repetition and lack of conversation.

You can go back, hunt down all the bosses, get all the skyshards, find everything. It will be slow, but you should get some XP for these.

Or you can try grinding against the creatures in craglorn, at VR13 they will be a challenge, but doable.