Why don'y you post a picture of yourself on or next to your bike and we can tell you if it's too small for you.
Bad fit (too small) is not synonymous with aching knees. If you had said your back was hurting then it would be much easier to say your bike is probably too small. If you had recently tried clipless pedals for the first time and your knees were now hurting that would also be easier to diagnose.
I imagine most bike shops will advise you to buy a new bike and then direct to view their range...
Why don'y you post a picture of yourself on or next to your bike and we can tell you if it's too small for you.
Bad fit (too small) is not synonymous with aching knees. If you had said your back was hurting then it would be much easier to say your bike is probably too small. If you had recently tried clipless pedals for the first time and your knees were now hurting that would also be easier to diagnose.
I imagine most bike shops will advise you to buy a new bike and then direct to view their range...