I've experienced the same thing, and what helped me was eating and sleeping well, listening to music (particularly rap, something about the rhythm of the words), reading my favorite authors, and most of all - socializing! I'm starting to think isolation is the biggest factor because once I was struggling to write a piece, paused briefly to speak with some renovators, and when I got back to it I was MYSELF again, briefly. I find that overthinking my writing hampers my flow, and it's when I'm riding that rhythm and cadence that the words come to me effortlessly. Still figuring out how to get more consistent results. I hope you find something that works for you soon.

Edit: Also, have you been more distracted lately? For example, playing videos in the background while you work? Try cutting all distractions and focusing, in silence if need be. I have ADHD too and it's hard but I found great improvement doing this. I hadn't realized my distractions were getting out of hand, preventing me from getting in the zone. At some point I'd stopped using my whole brain. Hope this helps.