I've had a gastric sleeve in less than a year and and at the same being treated for lung cancer and started putting the weight back on what do I do?

Don't worry . Your lung cancer treatment is top priority. Try not to worry about your weight. You need good nutrition and enough calories to get through treatment. And some of your medications may be causing your weight gain. Love yourself during this hard time, and know that we oncologists prefer patients to be hefty rather than gaunt during treatment! good luck!
Consult with surgeon. The sleeve should be helping you to lose weight. The lung cancer treatment may interfere if the mess go treatment are making you hungry. Either way you need to consult your surgeon to make sure you are nutritionally optimized. Also to make sure the sleeve is working.