I got an ultrasound on my left umbilicus because i experience swelling there after i eat and use the bathroom. it came back normal. what could be causing the swelling and fullness?

Hard to say: Assume you had the ultrasound because Dr thought you might have umbilical hernia: those usually do show up on ultrasound. Excess bowel gas might cause such symptoms, & simethicone (over the counter) can help. A food diary to see if any correlation between types of food eaten & the swelling might help pin it down. I recommend asking the Dr who ordered ultrasound what other tests might help.