What Are The Side Effects Of Oral Contraceptive Pills?

I have started using the Trigestrel oral contraceptive one week ago. It is the first time that I am using oral contraceptives. Since starting the active pills 3 days ago, I have been experiencing terrible tummy cramps, diarrhoea as well as nausea. My period, however, was normal, and a lot lighter than previously. I have seen many complaints for this product on the Internet, and I am therefore worried that it may not be the best option. Should I stop the pills, go back to the clinic, and ask for a different product, or should I endure the pain in the hope that the side effects will go away? Please help!