The hunt for a health plan that would cover a particular drug or a favorite doctor proved particularly frustrating for many consumers navigating the new insurance exchanges under the federal government's health care overhaul, according to a report released Monday. In nearly half the 85 health plans analyzed, it was difficult or impossible for people to determine what drugs were covered, according to the report by market research firm Avalere Health, the first systematic analysis of consumer experience on the exchanges. The report analyzed health plans in five states that relied on the federal HealthCare.gov website, as well as state-run exchange plans in Washington, D.C., and a dozen states.