Maybe its your balance? Just reading the part which said you had thrown them but the didn't connect well. Just throwing it out there but maybe you aren't setting yourself in the right position to throw them, this would explain how your body wont react. Check your feet that your on the ball and not the heels especially your back foot. Also practise using it on a light heavy bag where you can turn and rotate around the bag, in and out so you can simulate this.

Don't know if that helps at all, but was a major hurdle for me when trying to throw a hook after a jab.