As long as you're not having any abnormal stomach pain, and your stool looks normal, I wouldn't worry about it. Eating more veggies means that you're probably getting way more fiber in your diet than you used to get - which isn't a bad thing. Just remember to drink plenty of liquids as well. If it continues to bother you or gets worse, you might want to consult your doctor, just in case. Some plants hold more fiber than others, like most leafy greens, broccoli and such. Research which foods have more, then you can determine how much fiber you're getting in a day. You might just have to cut back on some of those things.