You would have to be seen in person to be properly evaluated. Pregnancy could impact the swelling and pushing on your incision.
I am sorry to hear about your concerns but online consultants, without the benefit of in person evaluation, will not be your best resource. Having said that, it would be extremely unusual for breast augmentation incisions to open at your stage. It is more likely that you are experiencing engorgement/swelling as your breasts change with pregnancy. Besides your own plastic surgeon, your OBGYN may also be a good resource for you. Best wishes for smooth pregnancy / delivery.
I'm sorry to hear that your surgeon is giving you the impression that he doesn't care, or is being dismissive to your concerns. I know it's not an excuse, but perhaps he's just really busy and overwhelmed, and his bedside manner and way of dealing with it is not the best. In any regard, if you are not able to get your concerns addressed by him, then it may be best to find another surgeon who can examine you in person and put your mind at ease. As I said above, it would be very unusual for a 3 year old incision to suddenly come open with pregnancy, however, as I am not able to examine you myself, and you haven't provided any pictures, there is very little else I can offer. This is something that should be seen in person. Sometimes the areola undergoes changes with pregnancy as it prepares for the breastfeeding of a baby. The tissues become thicker, darker, and enlarged, and sometimes little lubricating glands, called Montgomery glands, that are normally on the areola become enlarged and look like little "balls" as part of this process too. In any event, I think a board certified plastic surgeon with experience in breast surgery would be able to examine your breasts and give you a good idea of what is going on. In addition to being certified by the American Board of Plastic Surgery, your surgeon should also voluntarily participate in the Maintenance of Certification program administered by that board. This is the best way to know that your surgeon not only has the best training and experience for the procedure, but that he or she has maintained currency in the certification requirements as opposed to practicing on a "lifetime" certificate which has only been reviewed once at the beginning of his or her career. For more information on this you can visit ABplsurg.org or ABMS.org. Good luck.