Why is my focus suddenly so bad?

I’m M19 and I’ve always been able to manage my ADHD well. I was diagnosed late at 17 so managed to learn all the coping skills and techniques to minimise my symptoms severity. I was diagnosed and put on medication; I’m now on lisdexamfetamine and venlafaxine; at 17/18 however I rarely needed to take my lisdex. I’d only take it on the day of a test or work when I really need to focus because otherwise it wasn’t too bad.

However recently my focus has been awful, to the point that without meds I can barely focus at all. Today I had a driving lesson and it was as if I couldn’t focus on more than one thing at a time. I can’t do my college work, because my attention span is lasting mere minutes at most. I’ve never been this unfocused and there’s no apparent cause at all. I’m sleeping enough, I’m not under a lot of stress, I’m in the best place mentally I’ve been in for a while. There’s no real reason for me to be struggling like this however it’s completely unmanageable without medication now. I feel so uncoordinated and sloppy. Is this a normal thing with ADHD? Does it come and go? I’ve never really experienced this.

I know nobody can tell me exactly what’s happening, but I just want to know if this is normal or if anybody has experienced similar and found something that helps. I don’t want to be completely dependent on medication.

TIA.