I'm having a roller-coaster ride too. I can relate.
Bought a foil last August. Looked at videos and lurking here hours on end. 3 sessions in I'm still not getting up and I tangle lines in foil and cut a hole in the arse of my new wetsuit.
1600€ is Wasted???
Now it's late September and I break for season. I'm not happy with my overly buoyant T40 board and convert my surfboard for trip. In February I take 4 hrs private instructions in Mexico and get up flying with some control. I'm ready to solo and do 3 more solo sessions in Mexico
Back home it's freezing and 4 weeks later I'm back on T40 again in 3c water and can't see a thing with fogging glasses and can't get up at all.. hate the front footstraps
Get foothooks and back to my surfboard, go out 3 more times and have freezing cold choppy, solo sessions. But learning. 4 more sessions and really flying now!
Pick up a shoe at home and Bam! Back pain, the thing like you. 2 weeks off work, 2 weeks to get back.
Then only 30 min sessions for next 4 sessions in 2 weeks.. Get going doing 90 min sessions. On session 23-24.... Now and learning transitions.
My converted surfboard is really dragging on touchdown due to conversion plate, so I make a new board quickly. 2 sessions, hit a sandbank and BAM board folds.
Now I am waiting for a new board to arrive.... More money....
Have to convert an old experiment board so I don't miss the weekend - wind forecast.
I suspect my POS board will fail or I won't be able to ride it....
Happy my back is holding up anyway.