Changing BC to minipill

Serena

Hi, I just started using BC this month and realized that I got bruises on my legs and arms as the side effect. Turns out this is a rare case if u dont suit to BC pill. Fyi, I hv used almost half of the package of BC pill. Then, today I went to doctor and decided to get minipill. Will it effect my period cycle? And how effective it is to prevent pregnancy?