I am extremely obese. Can anything be done to lift my stomach? It interferes with walking, sitting and lots of other things.

Unfortunately, it's impossible to comment on your specific case without any photographs. In general though, patients with excess hanging abdominal skin that overlap/rub/irritate (pannus) and interfere with activity and exercise are often good candidates for a panniculectomy. This procedure differs from a full TT as only the skin and excess tissue below the belly button are removed.
Ideally, patients should be at their goal weight and stable for several months prior to undergoing any abdominal cosmetic surgery to obtain the best final results. If you haven't been able to drop the excess weight with diet and exercise alone and are unhappy with your current weight, you may consider consulting with a bariatric surgeon to discuss the various surgical options that could help you achieve your goal weight. Not only would this help in that regard, but lower weight/BMI correlates with better results, safer surgery and less post-operative complications for cosmetic surgery not to mention the long term health benefits of being at a more ideal weight. Best of luck 

Dear softandfuffly,the optimal weight to have Tummy Tuck surgery is a very common question and for good reason. Having surgery before you reach your target weight can lead to suboptimal results if you were to lose more weight after surgery.
Good first questions to ask yourself are:
1. Am I at my goal weight?
2. Is my weight stable? have you lost or gained more than 10lbs in the past month? What was your weight last year?
3.  Are you eating a healthy diet and exercising?
If you are not at your goal weight or your weight is not stable, you should hold off on surgery.
Daniel Barrett, MD, MHA, MS 
Certified, American Board of Plastic Surgery 
Member, Am. Society of Plastic Surgery