Late period last month; had a light one; then headed into being late again this month?

Okay so last month I was late by a week and when it finally came it was really light. Now if I am going my 28 days since the last one finally started, I should have started by the latest today, but nothing yet. I only had once this month because we were both so busy. So the likelihood that I would pregnant from this month is very low. So is is possible I could be pregnant from last month? I took a few tests when I was late and they always came back negative. However I kept getting a whitish/grayish line (evaporation line?) right away. I was told that evaporation lines shouldn't show up right away but only after the test had been sitting for a while. So could that have meant something? I haven't tested again since my last so called period. I am thinking I should wait and test if I am a week late again. This is just so weird for me. I am never late. I usually even spot the night before my period like clockwork.