Can I change from dual plane to fully under the muscle?

When implants are placed in a dual plane, the muscle is cut at the bottom of the breast.  Unfortunately when the muscle is cut, it cannot be repaired to place the implants in a true subpectoral position.  The problem you're experiencing may not be due to the position of the implants though.  I recommend following up with your plastic surgeon or getting a second opinion.  

No, changing implant position to complete sub-muscular is not likely to successfully solve your issue, and may introduce problems you don’t now have.  Recruitment of serratus anterior muscle to completely cover implants was long ago abandoned for good reason.Consider addition of substance over your implants such as fat (grafting), acellular dermal matrix (Alloderm, Strattice, Belladerm), poly-L-lactic acid (Sculptra), Galatea absorbable mesh, and/or a more cohesive gel device for more suitable consistency.