Could Shorter And Light Periods With Dizziness And Back Pain Mean Pregnancy?

I'm on the birth control pill, but from April 7-11, I was on an antibiotic (Zithromax z pack) and a cough suppressant with Codeine. My doctor told me that I needed to use a back-up method until I started a new pack of pills. I started a new pack on Monday.

My husband and I were together on April 11th and April 13th. I was due to have my period on April 15th. I did experience some bleeding, but it wasn't what I normally experience with my period. It was lighter and only lasted about 3 days. (My periods normally last 6 days.)

On Tuesday, I started experiencing breast tenderness like I've not had before, nausea, dizziness, trouble sleeping at night, and fatigue. As of yesterday, I also have a dull lower back pain and dull lower abdomen pain.

I've never been pregnant before or had any experience thinking I might be before, so I have no idea what to do at this point. Is it possible that I could be pregnant? If so, when should I take a home pregnancy test? When can I get a blood pregnancy test?