Yup that's what happened to me during my first pregnancy. I went about 8 months with no stretch marks so relieved and happy then one day bam there they were right around my belly button. Little lines. So small I could barely see them but in that last month as the baby dropped they grew longer. They didn't get too bad but yea they were noticable. I blamed it to the baby dropping or getting lower on my abdomen. So just try and keep ur belly hydrated with lots of creams.
Did you use lotion or anything?