Help with this hcg chart ? Pic

Okay confused? Today I am 5 days late according to this chart I would be 5 weeks today, since my last period was dec 27? I started counting on the calendar the 28th to today the 31st, which would be 35 days from the 27th of dec, my last period. So WHY am I still getting negative HptS? Should I go get a blood test? Having tons of symtoms I don't feel like typing out right now lol and I just feel like it's my month it was our first month trying OPks, and we used them successful, and I just don't think that I just happened to be 5 days late when we use OPks this month, when I'm regular and right on time every month and having all these symtoms Iv never ever had, What should I do. Also I'm 18 dpo and one thing does anyone know how a blood test is at the walmart clinic? Thanks!