My best friend had a 52 day cycle, basically she only ovulated every other month due to PCOS, if I were you I would try an ovulation monitor, I think it's cheaper than the individual tests and it will tell you 36-48 hrs before you ovulate which is when you really need to know, if after a couple of cycles you haven't ovulated go to see a doctor.
He will probably put you on clomid, which makes you ovulate, unfortunatly the monitor won't show your peak days after that, but hey, I know I'm just having sex every other day, got to hit the spot somehow!
I had the exact same thing happen as you. Tina1111's post describes how it worked out for me this last time. I ovulated really late, and now I am in my 2ww with fingers crossed. Best of luck to you. You will probably ovulate in a week or so.
Your cycle can vary greatly during the follicular phase (the time from period to ovulation) but, your luteal phase(time from ovulation to next period) should remain pretty constant from cycle to cycle. The luteal phase's normal length is from 12-14 days. If you count back from a 45 day cycle, you probably o'd somewhere between 28-31st day. Today would be CD20 for you. If your cycle is normally 45 days or longer, it is still quite early for a pos opk. If it varies, I would keep testing.
Some women have problems detecting their LH surge, even when they do ovulate. I think your best bet is to chart your temperatures. Charting won't tell you when you're about to ovulate, but it will tell you whether or not you ovulated after the fact. If you have temped for a few cycles and never see a bi-phasic curve (lower temps before O and higher after), you're probably not ovulating and should set up an appointment with a doctor. It's not uncommon to experience an anovulatory cycle once in a while, though, so give it a few months first.
You can reard more about charting at fertilityfriend.com. You can also register there and chart online for free.
Good luck!