Hi Carol and welcome to the forum,
You DEFINITELY don't want to eliminate a shake. Medifast is clinically designed to work as prescribed.
The plan is already very low calorie, and eliminating a meal can cause the bod to go into a storage mode for protection.
Some reasons for a plateau can be:
1. Cutting back on meals
2. Not eating regularly - every 3 hours
3. Interactions with some Medications - Are you taking any meds?
4. Not slurping all your water - Minimum of 64oz daily
5. Not getting enough sleep
6. Women stuff -
7. Stress
Reaching a plateau is not uncommon. This can happen after a steady, continuous weight loss. The body is just sorta taking stock of it's condition. This generally only lasts a few days up to a couple weeks.
Just be assured that you're getting a healthy, balanced diet and you're not gaining weight.
Have faith in the plan. Make sure you're not experiencing any of the above and you'll soon see those pounds melting away again.
All the best,
Unca