Car is leaking fumes following head gasket change.

Hi, I have had the head gasket replaced on my 03 plate Freelander. I took it back as it had problems and then had an injector replaced, at my expense. Since then I have been getting headaches and feeling dizzy - I took it back once and was informed that that coolant was leaking onto the exhaust, this was replaced (again at my expense), however I can still smell something strange and it is still making me light headed. I am now scared to drive my car - please help.