I'm suffering from constipation, and some time I get a headache and illness. There was also abdominal pain. Could you please tell me what's causing this and how I can get some relief?

Constipation and general digestive disruptions are very common with weight loss surgery. Many of us go out of our way to eat green leafy vegetables and/or take fiber supplements daily to keep things regular. If you do a search for constipation you will find many many threads with helpful tips.

I suffered with terrible constipation early in my journey. When it was really bad I had headaches, nausea and wicked belly aches. Once I started to drink like I did pre surgery, these symptoms mostly disappeared. I make sure to take a fibre supplement, which I detest, and now am able to add fruit and vegetables to my daily diet, I have almost solved my problem.

Constipation is actually fairly common, unfortunately. The headaches and illness part though I'd suggest calling your doctor and scheduling an appointment to get their take on that. They may have you do labs as it might be caused by a deficiency.