Your period can (apparently!) affect the taste of your milk, and it can definitely reduce your supply temporarily. So this may well be happening. But also, when you get to this age, your breasts don't tend to feel as full anymore and babies tend to nurse faster, so you might just feel like you have less milk, but you actually don't.
As for the cluster feeds, at this age, it often makes more sense to do them late afternoon rather than evening. The afternoon feeds might be 2.5 or 3 hrs apart and the morning ones a bit farther. But a lot of babies drop the cluster feeding by this age too. If you're doing a dreamfeed and he's eating well then as well as the other feeds, he might not need any extra clustering. I'd give it until your period stops and see what's happening then. HTH!
