I'm in the same boat as you but I work on web development instead of iOS.

I do not have a CS degree but I do have an engineering background. When I started reading SICP a few months ago, it felt refreshing. But I slowly lost interest as I progressed, for two reasons.

1) I had trouble understanding some math concepts mentioned in the book.

2) The exercises were getting difficult and I felt demotivated for not being able to take some extra time to solve them (I already have a regular day job).

I realised I had to get better at math first before learning more CS stuff.

So, now I'm learning discrete math for CS from MIT's 6.042J. I'm enjoying it so far.