I am 26yrs and I have missed my period for 3days now. I had tender breasts and abdominal cramps like since and my period have not come. I was on a pill for two years I stopped taking it for two months but it has been an on and off thing. Could that be the reason why my period has been delayed?

Period delays can happen for all kinds of reasons, one major one is STRESS. Take a breather and relax about the situation.
This happened to me last month and was a whole week late! Periods can be unpredictable :)
If you are more than a week late, consider taking a pregnancy test or heading to your doctor and have him look at you. It could just be stress. I know females who skip their periods for the month! I'm sure its nothing to worry about, especially if your breast tenderness and cramps are a normal sign you are getting your period.

Yes, taking the pill on and off could throw your cycle into mayhem, I would suggest either taking it fully again or not taking it at all. Also, before you started the pill, were you irregular? Because you could've just gotten into your old ways again.
Hope this helps and eases stress.