Aw i hear you. I had the same but not with colleagues. My colleague's have been really supportive but with my boss. Which had forced me to walk out and not return.
Sometimes people find it hard to understand and empathise when they haven't experienced things like this themselves. They can detach themselves.
I think this is where you feel icsolated with this illness.
Look to your friends and family or those who you are close to for support. I've recently lost my best friend due to being poorly for so long. But i am lucky to have good people around me still.
Have a look at the diet for endometriosis sufferers. I've recently cut out dairy and it has decreased the horrendous bowel pain in the mornings and at night.
Regarding work, i myself got to a point whereas i thought sod it. You dont care or appreciate that im coming in and working a physical job sick then i wont come in.
Maybe speak with your manager and explain again. That you really are suffering but you come to work so not to let everyone down.
I know how frustrated you feel. But doing your best is all you can do. And if they don't appreciate what you are doing then we sure as hell do.
Sending hugs xxx