Well done. I did my BSc with the OU and got myself a Diploma in Music along the way. I'm now half way through a Certificate in Business Studies. It was a couple of the early courses I did that got me into full-time university to study history as well.
If anyone had told me (or my teachers) that I would end up with two Bachelor's degrees and some not inconsiderable musical skill by the time I hit my fifties, we'd never have believed them, so much had everyone given up on me, so I know exactly where you're coming from in terms of your outlook.
Why not pick one of the subjects you've enjoyed the most and build it into a Certificate? You only need 60 points and you can fill most of those through 30-point and short courses at level 1. I'm debating myself whether to go for French or Maths next.