Cycles change for many and pills can be adjusted. For me, I can have breakthrough bleeding of my birth control pills with stress or due to a change in other medications. Other times, I have had tolerance build and had to go to a higher dose pill; or even needed them to be lowered. I have also had breakthrough from complications from other illnesses causing stress and hormone changes. The blood work will help the doc rule out any physical possibilities and to make sure that it might just be a change in hormones to adjust your dose. It is good the doc has ordered the blood work and the sooner you can go in, the better! Putting it off, only adds more anxiety thinking about it and not knowing. Really, go in and have one less thing to worry about!