Dull sensation in lower right abdomen.

Hello, I have been having dull sensation in my right abdomen for years now. It first started in 2011 when I was 17 years old. I got a colonoscopy then and it was normal and they said it was ibs. Then in 2012, it started again and I did an ultrasound and was normal. They put me on a to depressants and the sensation was gone. It keeps coming and going since then. In 2014, I had sigmoidoscopy for rectal bleeding and it indicated hemorrhoids and anterior and posterior fissure. Last July it started again and I got an ultrasound and it was normal. Since October 2018 I had on and off sensation in the same region and I visited a gastroenterologist who did crp and then fecal occult blood test both of which were normal. And now since the last three days it's started again and it keeps coming and going throughout the Day. This time it started when I came to high elevation (9500ft). What could this be?