I use a fiber product called Konsyl. You shake it with 8 oz liquid (I use about 2 oz whatever fruit juice the kids have around, a squirt of lemon juice, and the rest water) and drink it. Follow with a glass of regular water. It has never given me a stomach ache, but I've never tried any other fiber products so I don't have any basis of comparison. Might be worth a try for you if you want to add fiber.

Glad to hear the retest went better for you!