pull in the armpit

i used to go gym. i had built good body.but after 1 month break when i joined the gym and due to bad diet my body did not respond but i continued to go gym after doing workout for 3-4 months i stopped going gym and occasionally i continued to do exercise at home.there is always a pull in my armpits which keeps(which i suppose also pull the nerves of chest and back because i feel so the nerce pull in the midriff )my midriff thin and weak and the body doesnt respond and it keeps my midriff to  expand after exercise. i think it all happened when i lifted weight in dumble exercise for biceps. it is not permanent because 2 times my body  became normal 6-7 months back.