The sd card is not an extension of the internal memory. Apps and their included data is stored in the phone memory. You can move music, photos, videos and some apps that have a lot of data allow you to store the data on the sd card. It takes a lot of apps to fill up the internal memory unless they are some games that has lots of data it needs access to on the fly. You have to decide which ones are important. It is easy to reinstall an app if you need it occasionally and then delete it after you are through!
A search for SD Card or memory in this forum will find a lot of fixes and solutions other have found!