Loss of feeling of fullness after eating

First off I wanted to say that I had IBS long before this symptom started. I never had any surgery and I have been lean my whole life with a BMI probably averaging around 19.

Before this symptom started I would eat and gradually feel more and more full until I felt like I could not eat even one more bite. Then that feeling of fullness would gradually dissipate until I was eventually hungry again.

I started eating a vegan diet after I was seeing two doctors that were vegan and urged me to try it. That was the beginning of the loss of feeling of fullness. Also this was the onset of the loss of my sense of taste and huge increase in chemical sensitivities and feeling flu like constantly and suffering from exhaustion so bad that I'm completely disabled by it.

I first noticed that I was not feeling full after eating, This progressed to not feeling anything at all after I ate and feeling like I had the flu constantly. I also lost my sense of taste to the point of it being nearly gone.

I want to make this part clear I stopped eating vegan well over 25 years ago and this symptom never went away.

It's so bad that I use a timer after I eat so I know how long that it has been since I last ate because I cant tell, I can't feel it and I would just eat right after just eating. This has gone on for over 25 years.

I just wanted to see if anyone else has this symptom or knows what might be causing it?