This is great that you are busy!!
I had the same issue too for a good while and I put my prices up, and I also just let them book as far ahead as they wanted to, so long as they paid a deposit to secure the booking. Although it is good to prioritise regulars, the way I see it is that those regs made not always be there and you need an opportunity to grow more regs. My older regs figured that if they wanted to see me then they'd book well in advance.
If the issue is that you are being too accommodating (which I was very guilty of too and didnt realise until Ibhad worked 14 days straight), then decided which days you want to work, advertise those days and DO NOT veer from them no matter what. Your clients will learn that they need to see you on the days you choose to work, no matter how much they offer you.
I did find ways to reduce on the admin though which, for me, was the main thing I struggled to manage seemlessly. Automated text & email responses, online diary so they can see when you are available, etc etc. It helped.