Skinny stools and incomplete evacuation are due to spasms in your colon and common in IBSers. The only way to stop them would be to manage your IBS, which it sounds like you're trying to do. If you haven't changed anything (supplements) in a while, maybe these spasms and symptoms are due to stress or hormones or lack of sleep.
As always, if you're really concerned and this is a new symptom for you, go see your doctor.