the feeling of cannot breath is a normal symptom for pregnant woman esp in 3rd trimester. but if u still cannot breath in whatever position u tried, please seek ur dr. and for sign& symptom of labour, baby pushing and feeling of tightening is not the sign/symp. But if it is associated with PAIN,(regular& increase in intensity), / bleeding / leaking of water(gushing of fluid coming out/'meleleh kat peha'), these are the sign&symps of labour..