Ovulation bleeding

Emma
Do any of you get bleeding at ovulation time? And if so; how heavy is it compared to an actual period? 
The background for my question is that I have very irregular cycles and am having tests done to establish the cause. My doctor has asked me to come in for a specific blood test within the first five days of my next cycle. 
Now I've started bleeding but very lightly and without any cramps. I would say it's more than "spotting" though. It first started two days ago and have gradually gotten slightly heavier. Last cycle I had similar bleeding for about three days and marked it down as a period; but then I got a proper heavy period two weeks later, which makes me think the first one wasn't "real"
Any thoughts? Could I be ovulating or is it more likely just the start of a period? I don't want to mess up the test by going at the wrong time...