As others have mentioned, you can literally be "busting at the seams" because you are too big for your clothes and the seams are literally busting, but this phrase has another common meaning. It can mean "I'm excited". Basically, you're so excited you can hardly contain it and you're "bursting at the seams".

"I'm busting/bursting at the seams." = I am so full of food that I can't eat any more OR I have become so overweight that my clothes no longer fit me.

I can not accept another work. I am full of busy.

I think it means when you eat too much. Your pant and shirt seams are bursting.