How often are you testing? What is the cl when you test before adding bleach? How often are you adding bleach and how much?
Whether or not you need to shock every time you drop below range is not a hard and fast rule. Sometimes you can get away with too low of a cl reading briefly and other times you can't.
Test your pool again tomorrow morning within 2 hours of sunrise. If you have lost more than 1ppm of cl overnight, then you should shock the pool. If not, then it shouldn't be necessary.
I can't tell for sure from reading your post, but I kind of get the idea that you are maybe not testing regularly and as a result, your cl is getting too low. Is that right? I would suggest testing every evening for awhile and maybe even writing down your test levels in the evening, making notes of how much bleach you added and what level your cl was when you tested the next evening. This will help you identify a pattern with your pool. After a few days of doing this, if you find that you can make it two days without your chlorine dropping below 3ppm, then maybe you'll be able to test and dose every 2nd day instead of daily. You'll just have to learn how your pool behaves.
Is it normal to lose chlorine faster as the level gets lower? I can't say for sure, but I'd say probably. It makes sense that it would because once you get lower than the minimum chlorine requirement based on your CYA level, then something may start growing in the water and thus you'll use more chlorine fighting it.
When FC and TC are the same, that is good! That means you have no CC which you want to be 0 or at least no higher than 0.5. FC + CC = TC.
I don't know where you live but if you find after awhile that with a CYA of 40-50 you continue to have trouble keeping chlorine in your pool, then it may be appropriate to take it a little higher. Aylad (another one of the mods) lives in LA and her pool is in hot full sun all day. She deliberately runs her CYA at 80-90 (or maybe 70-80, I can't remember which) because without doing so, she can't keep a FC reading. This also allows her to only add bleach every second or third day instead of daily. Watch your pool's pattern for a few days and report back and we'll help you decide what is most appropriate for your pool.
Hope this helps.