For my 1987 f250 when I turn shows low engine oil pressure and after a few minutes down to zero and goes?

Hello everyone I have a 1987 ford f250 to which he did oil changes and filters a few months ago to take my little work and after about 20 minutes this will be under pressure from oil and I will turn off the turn and went back to take her home when I saw k reaches the needle down to zero and let it cool for three or four hours turned to light went off and saw the needle was Low oil and 15 minutes under zero and turn off anyone have any idea what happens Nose heated ninada my truck is only low pressure and I can do to fix it

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