
My bitches have always had their next season after litters exactly when I'd have expected it if they
hadn't had a litter. It's 7 months or so since the start of her last season so she could be due any time, depending on her individual cycle.
However there's also the possibility that she has an infection because males find the smell of infection very similar to oestrus and get very excited. It'd be worth having the vet check her out and possibly give a course of antibiotics.