Should I be concerned?

Hey guys, so my girlfriend and I have been using glow for awhile now. Our goal for the past 4 years we have been dating has been to eliminate any kind of factor that could possibly cause us to get pregnant. Glow has worked good other than the occasional inaccuracy. Her period for the most part has landed every 28 days. However, there has been times looking through her logs that she has had 31 to even 42 days between cycles. We strongly believe that we aren't pregnant because we religiously use condoms and IF we do decide to be risky, which we VERY rarely are, it's usually a tease for possibly a few seconds. Due to both of us knowingly terrified of becoming pregnant, my penis is usually half-way inside her. Also, before this 'tease', I wipe away every bit if pre-cum that may be on the tip and within my urethra to further eliminate a risk. Knowing that pre-cum can still cause pregnancy and knowing how acidic a vagina is, we believed her vagina would quickly kill any kind of sperm in my pre-cum that could have gotten inside her. As of today, her period has not started between the week that glow predicts when her period would have started. This is the third day past the end of the predicted period date. She has been having mood swings, impatience, acne breakouts, small back pain (not constant), small cramps (not constant). However, no blood. She has just moved houses which has had her stressed out. I know that stress can influence periods. We're just not sure. If she were to be pregnant, the only possible way would be from pre-cum, however, we did NOT have unprotected sex. My penis was inside her for literally 2 strokes before we both became scared and put a condom on. this was after I wiped away all pre-cum on and in my penis. I know this is a long post, I just want to include every detail I can so I can get a more accurate answer. We both appreciate the help.