My gastro is hesitant to diagnose crohn's, he suspects it but doesn't want to label it yet. he said it's very mild. shouldn't i start treatment? isn't this progressive,like it will get worse?

Crohn's disease: Peculiar information; maybe you misunderstood. Symptoms can be mild, but arguably there is no such thing as a "mild" case: all Crohn's is serious or can become so. And uncertain diagnosis is atypical. Have you had a fecal test for calprotectin? Negative is nearly 100% proof against Crohn's. If positive, you need colonoscopy and/or abdominal imaging. Keep working with the gastroenterolgist.