What do you mean you have to add wages separately? Did you get 2 W2s from your employer? The wages in box 18are not added together. In fact they could each be 100% of wages in box 1. If you have 2 entries on boxes 15-20 you enter them separately on separate lines.
Sounds like you got 2 W2s?
If the EIN number is the same and you work in more than 1 state or city, sometimes they will give you another W2 with the extra state information on it and the top part the same or not filled in. If this is the case, list one W-2 but include both state or local taxes on it. It will let you type in more than one line for boxes 15-20. Don't add the boxes together.