5ft 6" and 190lb; I'm 5ft 6" and 180lb with broad shoulders so shouldn't be far off your build.
I've been trained in the past in cockpit ergonomic assessment, and also have about 80 hours in Cessna singles - most of that in C150s and C152s. Whilst it's a little cramped, I actually think it's ergonomically pretty good, and slightly better than the PA28, although the PA28 does have a bit more shoulder and headroom.
Neck, back and shoulder pain are a classic symptom of stress, and you are doing something which is quite new to you. Also most new pilots struggle with the fact that you should only grip aircraft controls very lightly. So, my instinct is to believe that you are most likely suffering from a degree of self-induced skeleto-muscular pain, which will get better as you learn to overlap shoulders with your instructor slightly, and to relax much more about the flying - which let's face it, is a pretty alien environment at first.
It is usually best to dress to be slightly cool in the cockpit - being over warm tends to promote airsickness, as well as bulking you out a bit unnecessarily - you'll find that most (real) flying jackets are deliberately quite thin.
G