Getting comments about being tall, didn't before. feel 3 in. taller but in late 30s. no prior measurements to compare. what could causes be at my age?

Standing straighter?: You are not going to grow taller at this age - meaning that the growth plates of your bones closed years ago. You can be perceived as appearing taller if you have started to stand more upright & having better posture. You have herniated disk and leg pain listed as your conditions - have they been feeling better recently? That might be your answer.

Not sure: Even with acromegaly, where an adult may be producing too much growth hormone, usually the jaw, hands and feet growth dominates over actual height increase. Otherwise there really are very limited conditions that lead to an increase in height. Are you sure it's not posture related ? This is something that you may want to address with your primary care doctor.