Having pregnancy symptoms, but on birth control?

I have been on birth control for a little over 2 years now. My period has came at the exact same time since I have been on birth control. My husband and had sex on April 27th and I wasn't suppose to start my period until May 3rd and ended up starting on April 30th. So I started 3 days early. My period was lighter than normal. About 2 1/2 weeks later I had mild cramps in my lower abdomen like I was getting ready to start my period. I cramped for 2 days. No blood and my period wasn't suppose to start for about 2 weeks. I have been very tired here lately and this past week I have become emotional and I am not a woman that cries over anything. Twice this week I haven't been thinking about anything and when I started to talk I could just cry. Now I am suppose to start in about a week. Could I be pregnant even if I am on birth control and have taken my pills every day. There might be a couple hours difference when I take the pill each day, but that is all. I have talked to a nurse and she said to take a home pregnancy test and if that doesn't satisfy me to go get a blood test. When should I take the home pregnancy test? Do I have to wait to see if I miss my upcoming period?