If you're eating a lot of insoluble fiber, that adds bulk to the stool and can be tough to digest, especially if your body isn't used to it. Also, take a look at what you're eating along with the roughage: Are you eating anything afterwards with simple sugars such as fruit? The sugars in the fruit break down faster, and your stomach hasn't had time to digest your meal so the sugars basically ferment and cause gas and bloating. I used to eat an apple or banana for dessert after my meals and always wondered why I got super bloated afterwards and then I learned this.
Another thing to do is to take a fiber supplement. I know it seems weird since you're already eating a lot of fiber, but if you take something like Metamucil (psyllium fiber) it forms a gel in the colon and acts like a sponge. It allows for a quick, easy, and comfortable passing of stool and you'll feel great after (and your pants will fit better too!) I drink a glass of Metamucil every day. I also have a very lazy bowel, so no matter how much fiber I eat, everything just sits there.. My doctor told me years ago about Metamucil and it's the best advice I've ever taken.
Another thing you can do is take probiotics. These are awesome because the friendly bacteria help break down food in your gut. However, some types of probiotics can cause gas, so be careful. I recommend Bio-K because they have a drinkable vegan formula that's very tasty and has 50 billion live probiotic bacteria in each container.
Another thing that is great for bloating: Peppermint and ginger tea. You can drink these hot or cold with some lemon juice added and it will help ease the bloating and also act as a mild diuretic. I take peppermint tea to work because I have a desk job and sitting down after a meal makes it harder for the food to make its way through the digestive tract.
Taking a walk or stretching after a meal is definitely beneficial. Sometimes at work, I'll eat standing up. Everyone thinks I'm weird but it works!