Straight from the horse's mouth, so to speak, at the Mayo Clinic:
Anal itching is a common condition. The itch, situated in your anus or on the skin just around your anus, is often intense and may be accompanied by a strong urge to scratch. You may find anal itching to be embarrassing and uncomfortable.
Also called pruritus ani (proo-RIE-tus A-nie), anal itching has many causes, such as skin problems, excessive washing or hemorrhoids.
If anal itching is persistent, talk with your doctor. With proper treatment and self-care measures, most people get complete relief from anal itching.
To read further:
http://www.mayoclinic.com/health/anal-itching/DS00453Pressure in your gut could be anything, but you need to chat to a doctor.