Hiya,
My situation could well be completely different to yours but my most recent cycle was 40 (my longest yet previously they had been 28-34) but this time it went on and on, convinced myself I could be pregannt, then between CD37-40 I had brown spotting (like old blood similar to what you describe you have been experiencing, looked similar to what I sometimes get at the very end of AF but never usually at the start) anyway, after 3 days of spotting today (CD1) finally AF has started but even today its more brown with tinges of pink/red and not as much as I usually get but I'm sure it must be AF just a differnet/stange AF.. really strange never had anything like it before I usually wake up, have a slight pain, go loo and AF starts there and then full flow.
Have you spoken to your GP about your irregular cycles? I didnt know whether its something I should seek advice on and is of concern or whether its ok and not a prblem? so would be interesting to get your opinions / advice as your cycles sound as random as mine...
xx