It's really hard to tell we thought too. Rowan is just on her first at 18 months, so we've had 12 anxious and neurotic months watching for every sign, every mood change, her male Cav King Charles friends behaviour - the lot! Vet said not to worry and would do further checks at her next visit. Naturally it came at the worst possible time, in the middle of a family holiday with her wee Cavy pal in close attendance!!!! She started by peeing our bed - she never peed inside never mind our bed. She was only in our bed due to her whining and upset which obviously in hindsight was her season coming. Her vulva is completely different, very swollen and open, her rear 2 teats are very swollen and noticeable and after a spot for the first two days (which like you we were is it, is it not?) it's now full on blood. She's coping great except for missing her walks and vet advised us not to use any knickers/pads as she needs to be able to lick herself clean at all times to avoid infection. Hope none of you guys have to wait til 18 months right enough!