Since MyFitnessPal is integrated at the server level, sharing should be automatic as long as your app has been synced.  Syncing is fairly automatic in iOS but sometimes need to have the Sync function run in Android. 

Please note that workouts only share to MFP after linking has been complete.  Workouts share to the MFP diary as well as the news feed as long as you have used the same username and password when linking to MFP.  

Please confirm that you have used the correct MFP credentials when linking to MFP.  You can determine the username in MFP's site (www.myfitnesspal.com) -> in the top menu bar, there should be your username listed.  Is this the same username you used when linking from the apps? 

One option is to note the username in MFP, and unlink and re-link to MFP. Perhaps try on the web if it didn't work in the app, or in the app if it didn't work on the web. 

From the Web: 

1. Login to my.fitdigits.com
   
2. Click on the Partners option in the top navigation
   
3. Click Unlink Account
   
4. Then click "Link Account" 
   
5. Make sure you use the PARTNER credentials in the following screen (see above on how to check what username). 
   

From the App: 

1. Go to Menu (or Health)  -> Partners -> MyFitnessPal
   
2. Tap "Unlink" (if linked)
   
3. Go to Menu -> Sync
   
4. Go back to Partners -> MFP and link again
   
5. Menu -> Sync
   

For information on linking MFP and Fitbit, please view here:

http://blog.fitdigits.com/tips-and-how-tos/link-myfitnesspal-fitdigits/