primrose oil question?

I was able to find it in capsules, I took one the day before yesterday and yesterday at 3:30 am I was woken up by a contraction that lasted 40 seconds then I fell back asleep and another woke me at 5:40-ish... I took one yesterday before bed(same time as before) and no more contractions.

Am I doing the primrose oil correct by one capsule a day orally? Someone suggested to also insert one in my vagina, should I do that too? 

How does it work?