I would be tempted to soak it a couple times a day in warm salt water to get that to drain. Keep it wrapped up and clean otherwise and keep an eye on it.
You can tell pretty easily whether it is pus (infection) or just serum (not infected) by whether it is cloudy or clear. I would not go by color. Serum is often rather deeply straw-colored.
If it's infected, soak it at least twice a day in water as hot as you can possibly stand it that is totally-saturated with Epsom salts (i.e. you have stirred in enough that some crystals remain stubbornly undissolving), for like 10-15 min at a time.
If it is not infected, don't soak it b/c it just retards the old skin drying off and the new skin (inside the blister) maturing and getting ready to comfortably play the role of Actual Outside Skin Layer.
I have horses, and ride a motorcycle, so I don't go barefoot as much as I used to. It does NOT feel good to be stepped on by a horse in your bare feet. (Been there, done that.)
Abi ! How do you stand to go barefoot in the winter??? In the SNOW?? If I don't have my fur lined snow boots with two pair of socks I would freeze! Maybe Im just getting old!