Hi there and welcome.
Without seeing a video of your swing it is not easy to suggest what is going wrong. You seem to have an idea that your setup and basic swing has some problems so I guess you will start looking at these first.
Your inconsistency with
irons could be due to many factors but you should check your takeaway and position at the top of the backswing first, is there any tendency to fan the club inside or cup your left wrist? Are you flipping your wrists through impact, can you maintain a flat left wrist? Are you overswinging at the top if so try a more compact swing.
Sorry I cant be of any better assistance but I hope you can find the problem soon.