Is Fostair causing extreme fatigue and aching all over my body.

My asthma nurse decided to change me to Fostair from seretide about 2 months ago following three really bad chest infections. Straight away I was more wheezy than usual and didn't feel right.Had a telephone appt with on of our GPs who asked me to persevere with it because he thought it would help me better in the long run. Anyway I've gradually felt worse,I've got aching feet,ankles,knees and hips all the time,sometimes I'm dizzy and get bad headaches. Generally flu like symptoms. I've tried to self medicate with flu meds but no better.Any ideas?