I would seriously consider the suggestions mentioned of getting your thyroid checked. I had a very similar problem to yours growing up, and if there is only one regret I have—it’s that I didn’t get my thyroid checked.
I was chronically underweight for most of my life—to the point where people assumed that I was anorexic. I was constantly hungry and ate all the time however. I was also constantly agitated and jittery (though I called it “on the go”)
At about 20, I was tired of being scrawny and I started eating lots of protein shakes and high calorie foods to try to gain weight and it didn’t work. But when I was 25, I suddenly gained 10 pounds out of nowhere. I gradually started slowing down, I got severely depressed and I felt cold and tired all the time. When I was 30, I suddenly gained 50 pounds in a very short period of time.
I thought something was wrong with my thyroid, but my doctor was saying that my TSH levels were normal. I kept gaining weight and slowing down and feeling terrible. I finally went to a different doctor that measured my T3 and T4 levels and those were low—even though my TSH levels were normal.
She asked me if I were unusually thin growing up and I said yes. She said that it was very likely that I had undiagnosed Graves disease (hyperthyroid) and my thyroid was working like crazy until it finally “broke” and I became hypothyroid. I’ve gained almost 100 pounds overall, and it’s really hard to lose weight no matter what my diet is or how much I work out. It’s also caused a whole lot of other health problems for me that make the weight gain seem minor in comparison.
Get it checked out. Hyperthyroid also does a lot of damage—I found out I had some cardiopulmonary problems related to having my thyroid going overtime for so many years. It something you need to get taken care of—and probably better to take care of it before your thyroid gives out.