i think shin splints are more of a soft tissue injury -- littlerock had horrible shin pain when she first went away to soccer camp; she could barely walk but it was in both legs at the same time and motrin and massage helped. it disappeared in a week but it was serious pain and i was initially thinking tibial fracture.
i read alot about SF since i had mine in february. if you can pinpoint an area of pain on the shin..with your fingertip..a spot that hurts alot when it's touched, it's probably a fracture. fractures start as stress reactions which usually occur due to repeated overload, lots of speed work..or a.sudden huge increase in miles....i guess our bones need recovery time just like our muscles do and when we stress the muscle to the point of failure, the bones begin taking the 'hit' harder. it's my understanding that a SF takes a while to actually happen but it can 'fracture' during a run -- it reaches its literal breaking point i guess. i had lots of warning signs -- lots of top of the foot pain when i ran but i thought it was a shoe issue and kept running every day; it was nagging but not horrible. then one day, it just got severe and kinda went from all over pain to one icky painful spot and i couldn't even walk straight.

i think a SF will become a complete break if you totally ignore it and continue to stress it.
it was almost 16 weeks before my 'fracture' showed on an xray so don't depend on an instant yes or no from that technology. i had an MRI 5 weeks in and it showed what they call stress reaction in the area -- it was highlighted, cloudy compared to the rest the foot. if the MD suspects a fracture, i'd insist on some sort of cast immediately -- air cast or whatever, even if you wear it without knowing for sure. an MRI or bone scan are the best diagnostics for SF. i know people who stress fractured their shin and their metatarsals years ago and didn't cast it and they still have pain probably cuz it never healed correctly. as hard as it was to put that boot on and wear it everyday, plus a nighttime cast...it made a HUGE difference in about 10 days; i could feel healing as opposed to that nagging crap pain i had with every step.
oh, and
don't take motrin (any ibuprofen) for fracture because it has been proven to impede the healing process --- it somehow interferes with bone reactions. (some doctors will dispute) there are studies now that say it stops bones from strengthening when you exercise -- somehow it interferes with the bone process of rebuilding itself as its supposed to when you lift weights or run. i took motrin ALOT for years. i will never take that sh it again, no not even for cramps.

(neither will littlerock)
good luck frog, i hope it's not fractured but if so, rest and an aircast are really the only things you can do.
okay, i wrote a book
i hate when that happens.