people differ in symptoms. There are those having BP II who feel happy with mania or rather hypomania and others who have a pleasant start euphoric then it turns dysphoric after a short while.
I don't think there's such a thing as "not severe" bipolar disorder. The episodes of rage and anger are the manic side of manic-depression. Mania can be a high (pleasant if Type II, or as far as psychotic if type I) or rage/anger in either type. If these episodes occur very often, you may want to ask your doc about rapid cycling.
If you are on a low dose of it you may talk to your doctor about increasing it. If it is the only medication you are on you might need to add something in addition to the lamictal.
I was actually diagnosed with bipolar disorder by a team of psychiatrists. I do have other symptoms. Like I said, all my symptoms have gotten better with the medication, but the episodes of rage still bother me. I don't like feeling that way.
doctors would only know upon their experience. I have rage too occasionally once in a while. I am sure most BP pts have it too. Differential diagnosis is extremely difficult in medicine. Medicine itself is a difficult discipline. So many factors involved and books don't help you to understand what you have. It's all their clinical sense what doctors rely upon mainly. They compare what you have to what they saw before. Nothing else. Then they - with trial and error - write something which can be totally wrong though. The proof is they tell you return after 2 weeks say.
Why I am saying that is because I know many people who aren't BP pts yet they yell scream and get angry easily. Lamictal will also help them but benzo's will too. So if you have BP this might be some form of mixed state associated with your symptoms. If not they lamictal will help you.
If your pdoc diagnosed you BP just because of your anger then I propose you get another view from another one. Because everybody has BP nowadays. It's good in a way because this might encourage the scientific circle to verse more funds to it so WE truly BP pts may benefit.
BP is not just rage, it's plenty of other things it's a syndrome