The majority of aquatic bacterial illnesses, including Columnaris, are caused by species of gram-negative
However, Erythromycin only treats gram-positive
infections. So if he does have Columnaris, this wouldn't be effective. Likewise, antibiotics won't treat viral conditions, so if he has Lymphocystis, it won't work on that either.
Columnaris is opportunistic, meaning that the bacteria that causes it is common in aquariums. If the fish's immune system is healthy, it can often fight off infection. But if something happens to weaken the immune system, the Columnaris can gain a foothold. When this happens, it can be pretty aggressive. In other words, if the white region is spreading, and look like bits of cotton, then it's likely to be Columnaris.
Below is a photo of a fish with severe Columnaris.
If it's not Columnaris, it could be a viral condition such as lymphocystis (as mentioned), or a cyst, or a tumor, or even an external parasite.
However, cysts and tumors generally only affect ONE side of the body. So you'd see a lump or bump on the right side. Or the left side. But usually not both sides. (Unless the cyst/tumor was large enough that it had spread the width of the body.)
Since it sounds like he has two separate lumps, one of which broke off, then to me, it sounds more like lymphocystis. Another thing to consider is an external parasite. There are some that cause small white lumps or bumps. But the affected region sounded larger fairly large (the size of a BB is pretty big).
Is he eating ok now? You'd said that he was having trouble with the larger bloodworms. Is this something new? And if so, has it gotten better?
Lymphocystis can cause pimple-like growths on the body. If they occur on the fins, it's unsightly, but not a health-risk. However, if they occur in vital areas, such as the gills or mouth, it can make eating or breathing difficult. There's no treatment for viral conditions, such as lympho. About all you can do is support the immune system, provide good nutrition, optimize water and environmental conditions, reduce stress, etc. If that's done, then often the fish's immune system can fight off the infection, but it still takes some time.
If you can't get photos, another option is to go an internet search for that condition and view images. You might be able to find something that resembles what he has.....