Licking her feet!

Tilly is a week off being 6 months old and this week she has started licking her back feet obsessively. Nothing has changed with her routine and she's a happy girl but when she's sat in her bed she just licks and licks and licks.
Any ideas why she is doing this?
Her head has gone all lumpy too and is definitely growing, could the licking be a comfort thing?
tia

Anal glands or demodex?

Logan does this a lot, as does a lot of other members dogs on here. I think it's a boredom thing more than anything. I brought Logan to the vet about it initially but she said there are no health reasons as to why he would do it. It seems to be early in the morning or in the evening when he's bored lol.

Could be a yeast build up, could be because of the grit, it could just be a habit which she will snap out of, have you checked the nails and pads? Moo went through a phase of licking her inside leg and made it sore Xx

I have checked her feet and cannot see any grit, mud etc I'm between her toes. She seems to do it when she's tired but is fighting sleep because she doesn't want to miss out on anything. We are at the vets in a weeks time for her 6 month check and I will get them to check her anal glands

Its not going to be anal glands, but hay if the vets wants a feel

I would say its habit, just stop her when you see her Xx