I am wondering if you are looking across the field as a whole?.... or are you actually seeing individual alfalfa plants?  If you aren't out looking for individual plants, then that is something you should be doing.  It is possible that your stand did not survive winter.

However, the fact that your wheat is just starting to green up tells me that you are much further behind where we are at - and that may mean that the alfalfa has not yet broken dormancy. 

If you are looking at individual plants, and can see that you have a decent stand of plants, then I would not worry about it.  It will come.  But you should be making sure your stand is there.  That is the first thing that I would be looking for.