Numb Finger Tip

Three days ago (Sunday) I woke up and the tip of my middle finger on my right hand was numb. I can feel it, there is circulation etc, but it has felt numb for several days now, at more times than others. I had taken over the counter cough medicine the night before due to a cough I've had for a few weeks. I stopped taking the medicine because I thought it may have something to do with my finger tip, but I woke up this morning and it was still numb (Tuesday). I have had a previous shoulder "injury" as well, tendinitis of the right shoulder & it hurts every now and then when I do activities (I may have aggravated my tendinitis the Friday before this happened). Not sure if any of this is related. Any idea what is going on??