Stool culture test and antibiotic treatment. Talk with your GI.
Before that, maybe a cleansing enema.
Low-sugar diet helps in bloating. You may want exclude any sugary food (sugar, sweets, fruits, cola, any alcohol, beer and potatoes (starch)) from your diet for a week and see results.
Fibers are good in constipation but they produce gas - so think. Raw vegetables produce a lot of gas, also cereals and fruits. Maybe you should drop fivber supplements for a while, if you're taking them.