I changed the oil pan gasket and filter and now I dont have oil pressure on 2003 Chevrolet Express 2500

Took the engine oil pan down cleaned every thing up changed the filter l and filled it with oil before putting it back up ) on the pan put everything back together and filled the oil to the proper level and now I don't have oil pressure
Before I did all of this everything was working perfectly oil pressure was good didn't hear any ticking of the lifters nothing . The only thing wrong was the pan was leaking oil around the edge ! Was just wondering if any one had any ideas of was would cause this ?

Had you removed the oil pump pick-up tube for cleaning , by any chance?