Please Help - Confused About Good Fats

I am confused about the good and bad fats... I know eating fast food or cheeseburgers or something will throw me into a gall stone attack later that night. And I know eating the good fats (olive oil) will help pass stones gently and painlessly when I do a flush. My problem is that I have been constipated lately because I am eating so little fat in my diet. My question is, can I be putting olive oil in gel capsules and taking one in the morning and one at night so I will be getting more fat in my diet and so I won't be constipated? Or, will this cause my body to try and pass stones every time I take them? Also, can anyone tell me the difference between poly, mono, and saturated fats?? Are one of these the good fats in food? Thank you so much :)

Val