I had a gastric sleeve approximately 7 weeks ago but have severe nausea!

At seven weeks after a sleeve gastrectomy, it is not typical to have persistent severe nausea to the point where you can only tolerate potatoes and struggle even with fluids. While some nausea is common in the first couple of weeks after surgery, ongoing symptoms at this stage suggest that something else may be contributing, such as narrowing (stricture) at the sleeve, delayed stomach emptying, reflux, or sometimes sensitivity to certain foods and textures.
The fact that you are finding it difficult to drink and are relying almost entirely on potatoes is concerning, both for hydration and nutrition. This can slow your weight loss and also put you at risk for deficiencies. I would strongly recommend you contact your bariatric surgeon promptly to discuss these symptoms. In many cases, further evaluation with an endoscopy or imaging is necessary to check the anatomy of your sleeve and ensure there is no blockage, ulcer, or stricture.
In the meantime, try to stay hydrated as best as possible, even if it is in very small sips throughout the day, and continue to track your intake. Persistent nausea is not something you should try to push through on your own—it is important to be checked by your bariatric team to identify and address the underlying cause. The good news is that with proper assessment, many patients find a clear reason for these symptoms and are able to return to tolerating a wider variety of foods and continue losing weight safely.

Make an appointment to see your surgeon and his certified bariatric nurse or dietitian. There are remedies to help alleviate the nausea. Your surgeon may want to  check your gallbladder also if you have none.
Hope you feel better soon! 

It is not normal and you should contact your surgeon/doctor to see how to alleviate this. Some remedies are quite simple sometimes but it is best to touch base. I hope this helps. Dr. Alvarez