Postpartum birth control

I feel like this is a dumb question but oh well. My LO is EBF and I haven't had a period yet (he's 10 weeks). My obgyn started me on progesterone for birth control. Would the progesterone cause me to have a cycle even though I'm breastfeeding? Has anyone had any side effects from progesterone (good or bad)? I've only been taking it for 8 days and just had a little spotting for a day or 2 but that's it.