LH levels seem to be dropping as I get closer to my fertile window

I am so confused. My fertile window is April 23-28 and I have been religiously doing my ovulation tests. This morning during my first pee, my stick came up0. I don’t understand, could I be pregnant? We had a miscarriage 3/11-3/25 (completion) and started trying as soon as we could. I did take a pregnancy test two days ago and it was negative. I did have a period but it was short (April 14-16) so I feel confused. My period was right on track with how it was before I got pregnant. Any advice would be appreciated!