I have an odd, throbbing pain on the bottom of my foot below my 2nd toe. I'm diabetic. Trouble?

May be trouble! Patients with diabetes are at higher risk for foot infections and ulcers (skin breakdown), due to nerve damage, inadequate blood flow to feet, and impaired immune function (all due to high glucose). If you have pain under your toe, you need to be checked out for infections, or ulcers, or even bone fractures. Diabetes is the leading cause of amputations -- check it out before losing a toe or foot!
Potentially. See your doctor so that he/she can do a simple exam of nerve conduction (vibration and 10 gm filament) and feel of your dorsalis pedis pulse. Simple office exams that should be done to differentiate nerve, vascular or ulcerous conditions.
Throbbing. Any pain is an indication for an exam , especially when you are diabetic. See your podiatrist for help . Good luck.