irregular period

Okay ladies, my period isn't irregular like monthly but it's irregular in the sense that I'm not bleeding like I usually do. I took plan b I think on Saturday and had some spotting at the beginning of this week. Yesterday I had some actual blood come into my underwear and I've been wearing tampons since. When I pull them out there's like no blood. This isn't normal for me. Is there a chance that in pregnant? Should I take a test?