Hi, I Am 21 Years Old. I Have Been On

Hi, i am 21 years old. i have been on Microgynon ED Fe for 5 months. It contains 0.03mg ethinylestradiol and 0.15mg levonorgestrel. I noticed that the chemist also has a Microgynon 30 ED and that it is more expensive. My question is, is one drug more effective than the other at preventing pregnancy? why the price difference? and how effective is the drug i am on in general?
Also, is early morning nausea a good sign mid-cycle? i take all my pills correctly at the same time (6am) everyday, give or take 30 minutes. And i have not been on antibiotics or been sick in a long time.