Goodness me you have been working very hard, I'm surprised you've survived. I worked 18 days in a row once and that was quite enough for me. I'm so glad you've got a job with actual days off.
I understand about not wanting to lie in, I like to have planning and structure for all my days, including my days off (when I have a job). There are lots of things you could do, such as take up a hobby, start playing a sport or going to the gym (I go swimming), make a list of nearby places you want to visit (towns, historical sites, museums or whatever) and go and visit them, join a club or a class that runs on that day,or take an online study course in something you are interested in.
I'm sure more people will be along soon with more suggestions.