Hello all, newcomer here. I've been playing MCX360 for a few months I guess. I worked my way up to an enchanting table and spawner xp grinder to enchant my armor for a trip to the nether. Well, when I started out, I was getting good enchants. 2 or 3 enchants per item, all level III or IV and I was happy. I'm trying to finish off my armor and weapons now and suddenly I'm lucky to a single level IV enchantment. Two is rare, I haven't seen three in about 15 or so tries so far. I wouldn't think anything of it, if I hadn't gotten 4 or so items enchanted at the start with awesome enchants. Nothing has changed: Level 30, my enchantment table is fully surrouned in bookshelves. I'm saving before I enchant. I just don't get why I'm suddenly getting such low enchants and only one at that? Any help? Hope its just a noob problem...
Honestly, it's just luck. The enchantment system is set up based on setting up random odds much like slot machines (see the Wiki for a detailed explanation). Also, the following link gives you your odds of getting particular enchants on certain grades of tools at different levels of XP along with the odds of getting 2nd, 3rd, and 4th enchantments on the same tool. Your best chance for certain enchants isn't always at Level 30.
http://www.minecraftenchantmentcalculator.com/rev5/