I did not have a problem with weight gain, but I can help you a bit :o)
it may take a couple of months for you to get back to your original weight, as 20 pounds is a significant amount to gain. It will take a little while for your body to get back to normal and get used to not getting hormones every day. Your dizziness, headaches, and urination are probably a side effect of your body's withdrawal from the birth control. Give it a couple of weeks and you should be feeling better. Try to exercise more and eat healthy foods for a while, as that will help your body to drop the weight. Try not to lose too much all at once - I think they recommend losing up to two pounds per week, but no more.
You may want to look into birth control pills that do not have estrogen. There are options out there! Just ask your doctor about it. A lower-dose of hormones could help as well. I am using nuvaring, which has a lower dose, and I have even stopped having cramps and bloating!