Fiber is less expensive in foods like seasonal fruits and vegetables. For instance, right now foods like corn on the cob, peaches and watermelon are good sources and contain lots of vitamins, minerals, and water. Water is very, very important because fiber acts on its ability to bind water have move through the digestive tract.
If there's not enough water then things can "get stuck" and bm's will be smaller. So I'd be sure you drink at least 8 to 10 glasses of water each day. That will also help reduce the gas.
There's lots of great information at the National Fiber Council's website - www.nationalfibercouncil.org.
I hope this helps. Please let me know if you need anything else.
Pat Baird, MA, RD, registered dietitian