Could be the veil. There's a veil between the physical plane and the spiritual plane [Ethreal] the thinnest point is Samhain and Beltane. People usually start noticing more activity around this time. I've dealt with spirits since I was a kid and even I don't 'see' spirits all year.
Meditation, balancing your chakras, and energy work can help you. You can also try relying more on your intuition because it can strengthen your clairvoyance.