Racing a Half within the first year of your running career is not too high a goal for most people. Unless you are running too many miles a week, your body should be adapting to a modest amount of exercise, with plenty of time to recover.
My best guess without further information is that there is something about the way your foot strikes the running surface that results in more pain in that one spot. It could be an uneven running surface (ie: slanted road), the wrong shoe, too many miles, foot structure, hip structure or biomechanics. There are also medical conditions involving the ball of the foot. Sesamoiditis is an inflammatory condition involving a tiny bone between the first metatarsal head and the skin pad that defines the main "ball" of your foot behind the big toe. Some people also develop necrosis of the bone tissue in this area or degeneration of the fat pad between the sesamoid bone and the skin.
Al of these things can be important to a diagnosis of your condition, but before it gets too far along, you need to identify why the condition has developed. I assume it was not an obvious problem until you were well into your exercise program.
At this point, it would be helpful to have your running form analyzed. Some gyms, running stores, and physical therapists offer this service. It usually involves shooting a video from a couple angles while you run on a treadmill. Some therapists offer analysis of these vids by e-mail. There are also biometric sensors that can be strapped to your legs and feet to produce critical data about the motion of your foot that is then analyzed by computer. Either way, it can provide important clues about excess motion, like pronation, that can overstress the ball of your foot. Some of these traits can be easily assessed by eye in a running store, or even in a mirror if you know what to look for, but detailed step-by-step analysis is most revealing.
If you have excessively high arches, or walk in shoes with an elevated heel, the problems created can roll over into your running. Another condition that I often write about is Morton's foot, which involves a short first metatarsal. This is easy to identify just by looking at your foot in good lighting. If you scrunch the toes downward it is easy to see if the "knuckle" of the big toe (over the ball of the foot) comes up short related to the knuckles of the smaller toes, which should all be in a straight line, regardless of toe length. A high percentage of people have this "short ball" foot structure - including me, so don't be surprised if you do too. If you do, it is likely to cause problems for running that many others on this forum have had to deal with as well.
Remember that padding for shoes can be a double-edged sword. It might make you feel less pain in the short term, but cause excess-motion injuries later. Some shoes and braces, that are used to provide support and prevent excess motion, can actually restrict the natural motion of your foot, and increase the chances of injury. Not all pads or devices are equal.
To summarize, foot structure, running form, shoes, and running surface are all very important if you want to run high mileage races and train for them. If you need professional help, you can expect to consult more than one specialist and spend out-of-pocket, unless you have very good insurance. Might be a good idea not to mention that you compete in sports if you want it paid for, lol. Exercise is widely prescribed, but many in the medical profession draw the line at competition. Meanwhile, you can get plenty of advice on everything I have mentioned (and more) in this forum.
The most important thing to do at this point, in my opinion, is to hold off on your racing goals until the condition of your foot, and your running form, have been properly assessed. Better to take a little break now for a brighter future, than risk months of injury for a long race that could leave you limping for a long time.
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