Does this seem odd, or just a coincidence?

My ex boyfriend and i broke up about 9 months ago. Ever since we've broken up i've talked/ dated 4 different guys. Each one seems to fall apart at exactly 3 weeks. I don't get it, is it something that i'm doing or is it just a coincidence that they all ended at exactly 3 weeks?! Its totally frustrating && def a huge damper on my ego. Any advice...anyone else have this issue?