Trying to gain weight with insulin pump

Hi everybody, I have recently gotten back to my insulin pump for about 6 months now. I absolutly love it! but believe it or not I'm having difficulties gaining weight, I'm 104 and I'm 5'3 my Endo wants me to weigh at least 115, but i really dont know how to gain any more weight. It is really frustrating! I was thinking on making an app with a nutrionist so they can help me.

 I really want to gain more weight because everytime i change my pump site it hurts since I'm so thin. I'm only inserting my pump site on my stomach because that is the only place where i have more fat. Does anybody have any suggestions?