I'm 171-172lbs and eat 3200-3700 cals/day and (if you're a junior in high school) I'm probably 10-11 years older than you which would typically make my metabolism and BMR a little lower than yours. No mystery here, you just need to eat more. WAY more. Those strength gains are definitely impressive, I'll give you that, but to gain size you really are going to have to put down a lot more food than 2500 cals/day. I'd suggest upping that by 100-200 cals/day every week or so until you start to see the scale move again.