My Child Is 2 Years And 8 Month . She

My child is 2 years and 8 month . She is having constipation problem from last 3 months . She trys to stop it forcefully and if it comes it's hard. Initially she was having only problem of hard stool , than problem of frequent urination for few days . Now she has problem of stomach pain and vomiting from 2 days. We were giving her Evict till now but it is not showing any improvement. What do u suggest us ??