Possible pregnancy? Wishful thinking?

Jan 14, 2013 I found out I was pregnant after trying for 5 years (after my twins were born completely by surprise). One month later, I miscarried (yes! on valentines day). We tried for several months in which case during that period I obsessed over dates and times and charting etc. about July we said forget it as I was becoming depressed that I couldn't conceive...if it was meant to happen it would. so, i haven't charted anything, haven't timed anything. Usually, I have breast tenderness about a week prior to my period and some mild cramping. I thought it was kind of strange that I haven't had any lately but I was waiting for the 14th because that was the day I was to start my period. That is how regular I am! I am now two days late and still no tenderness or cramping. No period symptoms, no pregnancy symptoms. I am slightly more tired than normal. Usually I go to bed around 1230-1 and the last week or two I have been practically crawling up the stairs at 9 and I don't do anything different during my day than what I have been doing. so here are my questions: 1) what could be reasons that I am late and have NO symptoms of either 2) what are the chances I could be pregnant 3) when is it safe to take a test and know that the result is prob 99% so I don't keep my hopes up.