Pain near belly button

For the past 2 weeks I have began to have pain around my belly button that is worse when I stand, cough, sneeze, bear down. It begins between 2-3am and only on nights that I work. Has anyone else experienced this? I'm 20w3d now. I thought maybe it's just stretching but concerned that it only happens when I work... Just curious to hear from others. If it continues, then obviously I'll ask my OB but I don't want to run to her for every little pain or discomfort, especially if it's normal!