screaming and t. tamtrums all day long

I hope someone can send me in the right direction or help.  My daughter just turned 2.  I have taken her to all her normal doctors check-ups with only one concern over the 2 years and that was that she never slept through the night.  We have kept a close eye on her progression because her sister is on the autism spectrum.  She is hitting all milestones and seems to be pretty on track with everything other than her behavior.  We brought her to the pediatrician because she was having screaming fits since about a year old.  She doesn't seem to have the normal temper tantrums and eventually calm down-this goes on for hours, and happens about 3-6 times a day.  I know she is two, but everyone who sees her behavior thinks this is not normal.  I don't know what to do, the doctor seems to think there is nothing wrong with her.  Is this normal???  I am ready to pull my hair out because I do not know if there is something wrong and I should be helping or if she is just "one of those kids" and i have my hands full with behavior.  If anyone can suggest what i should do next or where to turn to, i would greatly appreciate it.  

[LRM1021]

If she is going on for hours, then you need to take her to a specialist-- either a psychologist or a psychiatrist. Temper tantrums in 2 year olds? Totally normal. Hour long temper tantrum in 2 year olds? Not typical-- you need some advice from a specialist who can tell you what to do there.