I have had a constant rectal pressure (urge to pass gas but not really stool I can feel there is nothing there) and abdominal pressure from last week!

At first I thought it was due to gasy stomach/intestines as my stomach do get gasy easily, but it will usually go away within the same day. It's been more than a week and it's still there. I did not have any change in diet or whatsoever, the only thing is I started taking calcium supplement (with calcium citrate, magneium oxide and vitamin D) 1-2 days prior to all this. I have stopped all the supplements I'm taking along with that calclium supplement 2 days ago as I've read that magnesium can cause stomach bloating, but my symptoms are still there (still bloated!).

I do not have history of problems with bowel movements and don't think I am having now, my stool isn't hard although I do feel like the amount of stool passed is smaller for the past few days. I get bloated esp after eating a meal or sometimes drinking, and I feel stitches around my lower abdomen sometimes. My anal area feels a bit irritated occasionally but it's mainly the constant pressure that's making me really worried. Any idea what this could be? Thanks!