I think I'm pregnant. Any advice?

Today I finished my last green pill of my birth control (orsythia). So I'm starting a new pack tomorrow. This pill was the last one for the third month. My first month, I got my period the third day I took the inactive, green pills. The second month, I didn't get my period when I took the green pills. I took a pregnancy test & it was negative. I didn't get my period this week even though I was supposed to. Should I take another test before I start a new pack of pills? I think I might be pregnant but I'm not sure. I just need some help! Please!! Any advice?