Any ideas?

Ok ladies, the month before last AF was on time, last month AF was 9 days late, this month AF was on time. Done a few pregnancy tests and they came back negative. Dr done one and it came back negative and said my period is irregular. That was the only time my period was late. Well now I'm having some pain around my belly button. Has anyone had this problem before? And the pain any ideas on what it could be? Thanks in advance.