Southern California’s housing market remained weak in September, with sales dropping for the third consecutive month — but the region’s median home price ticked up slightly. Sales of newly built and previously owned houses, town homes and condominiums fell 2.4% from August and 16% from the same month one year earlier, according to real estate research firm MDA DataQuick of San Diego. A total of 18,091 homes sold last month. It was the slowest sales pace for a September since 2007, DataQuick reported Tuesday. Sales have fallen for three straight months beginning in July, when the boost from federal and state tax credits on the market evaporated. Prices remained relatively steady as sales continued to move from more affordable areas to pricier neighborhoods. The Southland’s median home price was $295,000, up 2.6% from the month prior and 7.5% from September 2009, DataQuick said.