Is tamoxifen causing my shredded nails?

I completed treatment for stage 2 IDC seven months ago. I’m in remission and have been on tamoxifen for about six months. I’m at 10mg because I have been STRUGGLING at 15mg and 20mg. Brutally.

Despite this, I’ve noticed in the past six months that my nails are just shredded. Vertical lines, brittle, and breaking or splitting all the time. Toenails too. Is this tamoxifen, or the stress of cancer treatment last year (I did several rounds of egg retrieval), or both? I keep my nails pretty short and don’t do manicures, so there’s no chemical atrophy. I’m so tired of having raggedy talons. I don’t know what to do!