please help me, please comment.

I am terrified. I know this will seem silly, but please help.
I am on the pill, I take it every single day at the same time and I haven't missed it all this month.
Last month I missed my period due to stress and new adjustments and such. I took a pregnancy test at the end of that period and it was negative. This month I was careful, again I didn't miss or be late to pills. Also, every few months I end up missing my period for no reason so I am custom to this, and all the pregnancy tests have been negative. 
Tomorrow is the start of my period week. All this week I've been having PMS symptoms, which I always get but I can't stop thinking they're more than that and I'm pregnant. I am so nervous I won't get it and I cannot stop stressing out, which I know will probably make my period not come again. I can't be pregnant, I cannot have a baby. Please offer some advice or reassurance, I am begging you.