This is the best thing you can possibly do if you’re unsure of whether you are thinning or not, how bad it is, and, (should you need them/wish to start them), a good length to keep for a year while you let medication take full effect. The hair will be so short that you won’t see much shedding, (especially in the shower), which can help keep it from dominating your thoughts.
Additionally, it will give you instant peace of mind regarding whether or not you are actually thinning or not, the extent to which it has occurred, and the pattern you are dealing with. The anxiety of not knowing is far worse than any answer you may uncover this way.
It takes a lot of will power to go this route and it can seem counter intuitive for someone who really loves their hair to cut it all off temporarily, but I really think it’s the best advice for someone in the position you were in or that OP is in. I’ve definitely suggested it before, but it’s not a path a lot of people, (including OP), are comfortable with, but your post is a perfect example of why I recommend it.