Cycle for last 2months has been longer (37) than usual (31). 22 into this cycle had brown bleeding for 2days & normal period for 3days. now day42 & proper period hasn't arrived, have no pregnancy symptoms and 3 negative tests - could i be pregnant?

Unlikely : However GP visit to order a blood test will confirm/deny plus assess for other causes such as thyroid problems or polycystic ovaries + can discuss management options if simply dysregulated cycle

Unlikely: Urine pregnancy tests are remarkably sensitive. They can usually detect pregnancy after less than even 1 week. If you have done several tests, this pretty much excludes the chance of a faulty testing kit. It doesn't sound like you need to worry about getting a blood test.

Likely cystic ovary: Irregular cycles, from cystic ovaries, higly likely, pregnancy less likely with negative tests. Decrease carbohydrates to improve ovulation regularity.