Anemia... why have i got it when i eat very healthy ?

ok.. years ago i was told i have pernicuous anemia and i have the B12 injections every 3 months - this week i have been told i now have a different type of anemia as well and ive been prescribed ferrous frumerate tablets 3 times a day. I dont know why my level is sooooo low??? I eat a very good mixed diet of fruit, veg, grains and meat. I feel exhausted, cant stay awake, my skins gone dull and my hair is lank. I have sores in the corners of my mouth. This has come on very quickly over the past few weeks. I have also noticed that under both armpits are so sore... i think its my glands?? I had blood tests done for thyroid, liver etc.. they came back ok... im confused :(