Delayed Periods

i m a mother of 11 months old. she is not breast feeding. in april i got my periods on 12th .till that i have a regular 28 days cycles. but after that i got my next perioda on 28may i.e 47 days cysle. i do urine pregnancy test and beta hcg but they both were negative. now i again missed my date . i check yesterday via strip but it turns negative. i m 5.5 feet .weight 69. and dlfacing alot of hairfall . i want to ask gaenycoologist what would be the reason for delayed periods. kindly guide me. thanks