I have been regularly taking birth control for 10 years, and I have never been this late with a period. I have had delayed starts to my period a few times, at very stressed out points in my life, but never this delayed. I am scheduled to start taking my new pill pack tomorrow and I have not gotten my period. If I am pregnant I do not want to casue any harm to the fetus. Should I or should I not take my new pill pack starting tomorrow, and what steps should I take next?
Also I should mention that my last period scheduled to start on a Sunday, did not start until Thursday evening, was very light and ended that Saturday morning.

I have been frequently urinating and very thirsty for the past month and a half or so. I had also been very active up until a couple of weeks ago I started feeling really tired and worn out, and I could not muster up the energy to go for a four mile walk like I normally can.
I get nervous the more I type. I am also experiencing lower back pain. Please let me know what you think! Thank you.