Hello Ken,
You have come to the right place for answers, the reason you cannot go to page 2 is because there is no page 2. This is indicated by 1-50 of 37, meaning the first page will show 50 emails, however you only have 37 emails in your primary inbox so the one page is displaying all of your 37 emails in the primary inbox. It will function like your social or promotions tab do, once you have over 50 emails then you will get a page 2.
I hope that helps.