Startup Oscar Health Insurance Corp. lost $105.2 million in its New York and New Jersey businesses last year, a sign that insurers of all sizes are struggling in the new markets created by President Barack Obama’s health-care overhaul. The losses, $92.4 million in New York and $12.8 million in New Jersey, were disclosed by Oscar in filings with state regulators. Chief Executive Officer Mario Schlosser said some of Oscar’s losses stem from the cost of starting a new health insurer. Others are tied to the same problems befalling bigger health plans: costlier customers and a shortfall in a key government program.