Wa'alaikum assalam! Honestly, kalau baby still moving okay and you're not in pain, biasanya it's just Braxton Hicks (practice contractions), very normal especially towards the end. But since this is your first baby and you're worried, better check with your doctor or midwife just to be sure everything's fine, okay? They can listen to baby and confirm semuanya good. A few of my mum friends had the same thing and doctor said it's just baby getting ready! Don't stress too much, just get it checked out for peace of mind.