I recently lost a lot of weight, and with it a lot of my hair. Is there any way to grow it back without gaining the weight again?

TE. Any significant change in your body such as a lot of weight loss can trigger shedding of hair by causing your hair to move from the growth phase to the resting phase. This is called telogen effluvium. It's nothing to worry about because your hair will grow back as long as you are eating well-balanced healthy foods. You could try biotin supplements and topical Minoxidil 1ml twice daily (2% f;5% m).