late period

Grainne
i had my baby on the 19th off june... im not breastfeeding so i got my first period on the 5th off augest... my second period came on the 2nd off september and my 3rd period came on the 4th off october... i was due my next period on the 31st off october and i hasnt came, so im currently 3 days late... took a pregnancy test 2 days ago and it was negative... me and my partner have been using condoms and none have split... i will test again in another week but im just wondering if periods can be irrugular even almost 5 months after giving birth? i also found out on tuesday i have a uti could that delay a period? thanks