Trying all I can

I (26 F) have always been on the very low end of the weight scale, though my family will tell you I can sometimes out-eat my brother. I hit 100 pounds on my 18th birthday and in the blink of an eye I was back into the low-mid 90s. I've tried protein shakes, vitamins and working out for muscle build up, and honestly I took a long while of being lazy and eating so unhealthy (not helpful in any way shape or form for literally anyone, even in my shoes). I'm over it, not even insecure about it anymore, it honestly just makes me mad. Does anyone have any advice on how I can slow down/regulate my metabolism?? Even if I've tried it before, you give me a different take and I'll try it again.