Multiple Postive OPK's and now lower back pain..What could this mean?

Hi, I got my period october 5th (Monday). We started bd'ing on day 10 and have bd'd every otherr day since then. I started the tests day 9 b/c i have short cycles (usually 25-27). Most came back negative but starting around day maybe 17 they became darker. I bought the 1st response opk's on day 19 and I seemed to get a positive. I wasn't sure so I kept testing everyday. Each day the lines get darker. It is now day 22 and the test line is the darkest it has been and I am now having back aches and some light twinges in my lower stomach. I am just confused because every other month my test are positive the one day and the following days they go back to negative. This month it is not the case... Could I maybe have ovulated sooner than the tests say and maybe be pregnant?? Has anyone experinced this? Any help would be great! Thank you!!!