I think that your chances of being pregnant are slim to none. Condoms, when used right, are very reliable.
To me, it sounds like you're dealing with ovulation symptoms which can include pain around the ovaries and lower back pain. Some women will even experience nausea, tiredness and bloating so it can feel confusingly similar to pregnancy symptoms. However, the timing you noted here goes right along with ovulation since that happens halfway through your cycle (around 14 days before your period is about to begin).
It's not unheard of to get these symptoms before ovulation takes place either, as your body gears up.
Keep using protection, properly, and you should feel comfortable knowing that your chances of getting pregnant are really low (according to Planned Parenthood, this method of birth control is 98% effective, so that's pretty good)!