Oo normal yan, mama! Maraming kaibigan ko na nagsabi na biglang nag-flatten or naging protrusive ang kanilang belly button nung pregnant dahil sa umuusog na baby and stretched skin, some even nag-pop out completely, which was shocking for them haha. Since you're already 34 weeks, best check with your OB lang para ma-confirm kung normal lang talaga siya or may something else na hindi okay, just para sa peace of mind mo, okay? After delivery naman usually bumabalik siya sa dating estado though it takes time, so don't worry too much pa!