Could my breast implants be causing my right arm/shoulder to feel dead, have sharp pains, nausea, headaches and chest pains ?

but no one can say for sure... but if you're too large and you want to be smaller, you can certainly do that.  If you want to find out if your implants are your cause, you can simply have them intentionally deflated in the office to remove the volume and if the implants were your cause, your symptoms will resolve.  If not, then you have other issues and now deflated implants but at least you will not be top heavy as you describe yourself to be.

This is a complicated question which requires a more extensive work up than what could be offered for you in this format.

Its unlikely that your implants are causing your symptoms.  I agree that they could be causing back and neck pain.  It is possible to remove and replace them with a smaller size which may help your back and neck pain.  Best of Luck.