My head feel heavy and my back neck muscle tight and i have flu last days now it is better?

Myalgia: can be from flu.. Tylenol (acetaminophen) or Advil should take care of the rest- if not improved within 1 week- see your physician.

After the "flu"...: If you were suffering of the flu or a similar type of illness even when it is resolved your muscles may stay sore for a few days and it should resolve soon as long as everything else is doing better. Continue with the recommendations given if you saw a doctor for this and if not drink plenty of fluids and rest while you are still feeling sick. If worse try to see your dr. for evaluation soon.