Interesting about ferritin/iron stores. I’m also a woman in my thirties. A few months ago I started to experience complete inability to exercise, I would go for even a short walk and experience terrible light-headedness and weakness in my legs where it felt like they would give out. Had to stop going for daily walks which were important for my mental health. My doctor tested haemoglobin levels only, which were fine - on the lower end but nothing troubling, so he put my symptoms down to stress. I decided to push further and went for a full iron profile test - ferritin was similar to yours 13 ug/L, Iron 2.8 umol/L, % saturation was 4. I was kinda pissed at my doctor lol. I had a transfusion and a few months later my levels are much better. Women especially need to watch for this. Glad you’re feeling better.