What Causes Light Periods For 2 Weeks?

I was telephoned by my doctors receptionist to arrange a visit as he wanted to see me. I went the following day and my doctor felt that l needed an ultrasound scan and a check over by a gynecologist,, this was due to my last visit to him l happened to mention that l had seen a period ( had not seen one for 6 months) which lasted around 2 weeks but very light. I had a cortisone injection and he feels it might be connected with this,, but what worries me is whilst out today my local hospital telephoned me, the urgency in the response has worried me. My doctor mentioned ruling out a few things thats why the check up was necessary. Could you enlighten me a bit more please ? Thanks .