Here are a few possibilities. Firstly, the delay in your cycle could be due to some transient hormone imbalance
or an unidentified pregnancy
. If it was a pregnancy, you could detect it through a blood test
as urine test is of no avail now. if not, the heavy flow is usual for a delayed period. Secondly, the pain could be due to either a tubal spasm
or a ruptured ovarian cyst
as often happens during a period owing to increased perfusion. While tubal spasm can be relieved with anti-spasmodics, ruptured cyst needs management based on the extent. A sonogram often helps. Take care.