My income turned out to be much lower than expected for last year and wouldn’t be eligible for subsidies. Will now have to apply for Medicaid. For the months of Jan, Feb, March of 2015 still getting subsidies. Will I have to return them and lose my insurance, then apply for Medicaid ?
Generally you can only owe back tax credits if you gain income, not if you lose income. So if you go from Marketplace to Medicaid and claim under 100% of the Federal Poverty level you'll owe back nothing.
Learn more about repayment limits here.