The process of breast atrophy or shrinkage after pregnancy can be worsened by breast feeding, but doesn't necessarily require breast feeding, so don't beat yourself up over having breast fed for 2 weeks. It is mostly hormonally determined.
If your implants are purely saline, then you will not be able to increase their size without having surgery to replace them. Four or five years ago an implant type called a "Becker" or "post-operatively adjustable" implant was available. This implant type contains both silicone gel and saline, and as the name suggests is adjustable after surgery to different sizes by adding to or removing the saline component. Your plastic surgeon should have records of the type of implants that you have. Check with him/her to find out if they are "Beckers", and if so, perhaps you can indeed have them increased in size.
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