Seriously though, lube is the obvious answer. Not a water based one, that’s shit for clit masturbation, it’s designed to go IN, not on.
Lovehoney have a big ‘blowout’ sale where their silicone lube is £3 which is just ridiculously cheap (that’s the UK site anyway). Also on sale is their ‘release’ lube which is fucking amazing. It’s really designed for handjobs, solo or shared but it’s amazing on clits too. If I didn’t have five tubes in the bedside drawer (not a joke) I’d be stocking up right now.
(That’s about three hours worth, don’t use that much!)
Beyond that, if you’re getting sore it suggests you’re going finger powered, so try a vibe (again, from £2.50 in their sale…).
It can be a real challenge to get used to doing it yourself if you’re used to someone else controlling things but I think it’s great to explore your own self control. No one will ever be able to edge you better than you can yourself – you can take yourself closer and know just what you can cope with, in a way no dom could.
I hope that helps!