I think I may be developing diabetes. I'm overweight and just started a diet. If I wait to check it out til I drop some pounds would it cause harm?

Can do both. If u can, cont. Lifestyle changes and chk f/ diabetes at t/ same time- bc if u find out u have diabetes and start treatment (which can be as simple as a single pill if diabetes is mild;ask f/ weight neutral med ), the treatment can be stopped if the sugars improve with successful weight loss of 7-10% of ttl weight. Also, treating diabetes may increase energy -> more successful at losing weight.
Possibly. Is there family history of diabetes? Do you have blurred vision, feel hungry and/or thirsty all the time or have to urinate a lot? Those are common signs/symptoms of diabetes. Getting checked can bring early treatment & help delay long-term effects of the disease. Weight management helps manage blood sugar levels, too. Best be safe and get checked now rather than wait until damage occurs.