I would suggest you start with enzymes. There are a number of good quality digestive enzymes on the market, get a broad based one that contains enzymes for carbohydrate, protein and fat digestion. Take them before meals for six weeks. According to my Naturopath many people develop problems with long term enzyme supplementation because the body gets lazy and does not produce its own enzymes. If, after six weeks, you find your digestion is still poor you can try an oxygen product or a specialty product like Okra Pepsin E3 that focus on clearing excess mucus from the small intestine. I also suggest you try either Liver Flushing or a good herbal liver tonic. Most of my digestive problems were eased with regular Liver Flushing and passing literally thousands of stones. I don't know your age or lifestyle, but anyone in middle age or younger adults with a history of poor eating habits have a good chance of having a congested liver.
Since this is the oil pulling forum, let me remind you that regular oil pulling will help detox and cleanse the blood, in turn, that helps the whole body. The oil will also help stimulate bile production which aids in digestion, especially fats. There is rarely a one supplement or one cleanse cure all quick fix. You will probably find it will take a variety of cleanses and short term supplement use to bring back optimal health. A clean colon, uncongested liver, and enzymes should all help along with the most important factor of all, a good diet balanced to meet your unique needs.