This happened to me in a pretty bad way last December going into January, and I can say pretty confidently that Protein and Biotin are NOT the be-all, end-all nutrients your body needs.
I did a lot of reading on this, went to doctors, and learned a.) Everyone reacts to anesthesia differently, so frequently the trauma of going under will sneak up on you and put your hair in a shedding cycle, b.) A side effect of rapid weight loss is your body hitting the panic button, because it thinks you're DYING, so it reroutes critical resources away from less important things like hair, and c.) Vitamin deficiences are an unpredictable beast.
I dunno if you've considered this, but you might well be Vitamin D deficient. I went in for a CBC early last year, and I was "catastrophically deficient" for Vitamin D. It was winter, the sun went down early and I worked full-time and went to school full-time indoors. I rarely saw the sun, so between my body not making enough of it and not drinking nearly so much fortified dairy and juice as I did pre-surgery, my system pretty much shut down. If you're noticing your nails are also really really brittle, that's another sign of deficiency. Your hair and your nails are made of the same thing, after all. But for sure, go to your doctors and check? Nobody here is claiming to be a certified medical professional, so consult your doctors before doing anything drastic or panicking too much, okay?