Problem with anal glands in my dog

My dog is having to have his anal glands expressed very frequently.  He does not scoot but does lick his anal area.  On several occasions, the vet noted blood when expressing his glands.  His stools are normal and he is on a hypoallergenic diet.  What could be causing the blood?  

[Jaybay]

Sounds like he now has an abscess from impacted anal glands.  Was he put on antibiotics?  Since you're having to express them so often, you might ask your vet if they can be surgically removed.  It might cause more trouble than it's worth - I'm honestly not sure.