1995 BMW 525i

Towards the end of last year I noticed my car developed some sputtering & hesitation when intially cranked - did not go straight to a smooth idle anymore. I initially changed the plug & this helped the sputtering for about a month, but never did anything to restore the gas mileage.
At this point I took it to the mechanic who replaced one of my engine coils & then noticed steam coming from my exhaust, which he said indicated that my head gasket was blown. That was also to have been fixed. Since initially taken in, the car has had to be returned to the mechanic twice for the same symptoms & occurences, without success. Though my car never ran hot before, now the Coolant level & temp indicators are daily occurences.
With that said, I don't trust the diagnoses being maide & would like some input on what 'the experts' may think. I would appreciate any possible insight. Thank you.