No, in general, once you sign up for a plan, you are locked into that coverage for 12 months, or until the next open enrollment period. A change in health status doesn’t make you eligible for a special enrollment period. However, in most states, if your income is below 150 percent of the federal poverty level you may be able to qualify for a special enrollment period and switch to a silver-level plan. Check with your state's Marketplace to see if this special enrollment period is available to you. (45 C.F.R. § 155.420).
On Private Health Insurance Coverage & The Health Insurance Marketplace