Memorising is as much to do with being able to "hear" what you are going to play and be able to reproduce it (no need for perfect pitch) as just knowing by "finger memory" and patterns. I usually learn patterns very quickly, how one sequence leads into the other, but important is too that each individual tiny fragment is memorised without fault. It's a bit difficult to explain, but I'm sure you could learn to memorise while learning the piece, and if you're playing a concerto, you must spend a lot of time practising, therefore, time where you could be memorising it. It should really be part of the learning process, not something you do separately, and involves a lot of concentration and listening to what you are playing, not to what you are imagining in your head.
Do you live in France? I did solfege for years, and it helps in some things, like listening to harmonies of pieces as you're listening, but I found for actualy performance and sight-reading it was completely against my way of approaching a piece. I suppose I always just learnt off by heart and then practised, which is not a good way around it since I got a lot of finger memory stopping any progress I could make...
Trying to memorise after you've learnt a piece is for me like learning it a second time around. I don't know if this might help, it's quite useful for a lot of things, but if you do read it, make sure you personalise everything it says, and adapt it to your style of playing (attachment)
hope it helps