Basically my period was about a week late (give or take a few days). I've had some symptoms (nausea, change in appetite, fatigue, etc) but I've also been stressing. The stress has only been for a few days. I actually started getting stressed about the time my period should have started. Anyway, it's been almost two months since the "slip up." I took a home pregnancy test last night and it came out negative. Someone informed me I should have taken it when my period didn't start (again, it's been about a week) and that I should take another when my period is over.
My questions are 1) When would be the most effective time to take another test? And 2) is there a possibility that I could be pregnant or did the stress just screw up my cycle?

It really should not matter when you take the pregnancy test, as long as you do not take it too soon. If it has been over 2 weeks since the possible implantation it will show up on a pregnancy test. I would say it is very unlikely that you pregnant. However, for conformation you can take another at home pregnancy test now or next week. It should not matter or effect your results.

The stress hormone cortisol can do amazing things. Making your period late is like lifting a finger for cortisol considering the other impacts it can have. I wouldn't worry.

Actually it does, the home pregnancy tests give a better reading, first thing in the morning, with the first urine of the day.

You want to wait about 10 days after you have missed your period to test.

I am confused, have you missed one period or two period ?
If one, how late are you now ?