First post. What do you guys think?

So my period ended 4 days ago, and I'm using OPKs for the first time, and I have some questions. Do the test lines get progressively darker the closer you get to ovulation, or will they be lighter or darker depending on the day? I'm only on day 7 of my cycle, but my CM is already pretty stretchy. I don't think I ovulated last month since that was just my second cycle after my mirena came out, and I never got stretchy CM, so it was a surprise to see it today. Is it possible to ovulate so soon after my period?