What Causes Sharp Pain Under The Ribcage Post Treatment For Sinus Infection?

My fifteen year old daughter is complaining about sharp pains in her left hand side of her lower chest, under her ribcage. She s been sick and was treated with a Z-pac for sinus infection. She coughed a great deal for the last few weeks but the coughing subsided 3 days ago. She could have a pulled muscle but her behavior has been altered, i.e. she doesn t want bend over to pick up things due to pain. My doctor s office is closed. I gave her Advil and a heating pad and it seemed to give her some relief. Should I take her to the ER or wait until morning?