It's simple. Bandwidth is limited. Many more people have gotten Verizon 4G devices in your area since you first got yours. Thus more of the limited bandwidth Verizon has is being used. Also many of them could also still be on unlimited data which of course would use up even more of the limited bandwidth. Verizon is installing micro towers in NYC as we speak so that should help by the end of the year. They are also going to be deploying LTE over AWS spectrum which will help those with devices that can use that spectrum. The Iphone 5 isn't one of them. The GS4 however is.
Too many people think mobile data is some unlimited resource and that everyone should be able to use it as much as they want. The fact is the opposite is true. Verizon has maybe 3% of the capacity they need to be able to offer a 12 Mbps in an unlimited fashion to everyone on cell tower. Maybe within 8-10 years Verizon will have this capacity and they will be the first.