As a homeowner myself, there is no way to answer that question with the information you provided. Its like asking a mechanic to say whats wrong with my car when its sitting in your garage.
You need a soil test done first. Dig up some dirt from around your yard and send it in for a soil sample. Probably the local univerisity would be able to do it for you. The results should give you fertilizer and lime recommendations plus times to apply. Once you know what type of fetilizer I'm sure someone will post which one they like best. Keep in mine most people on this site are not using the stuff you buy at HD or Lowe's so you probably won't be able to get it without a license. Post of a pic to two of the weeds and I'm sure someone can identify them for you. Once you know what they are, go to tractor supply and get the correct weed killer and fertilizer.
Cub Cadet GT3235