3 year old on the spectrum?
 

I have three year old twins (girls, fraternal) and I'm worried about the behavior of one of them. The main concern is her tantrums. They don't seem typical. She can go from perfectly happy to throwing herself in the floor screaming in an instant if she perceives something as not going her way. For example, if I close the bathroom door and she comes looking for me. As soon as she sees it's closed, she goes into full tantrum without even trying to open it and see if she can come in. I have three children and her tantrums are way more extreme than her sisters tantrums.

Another issue is her car seat. She always complains that it's too tight and will scream/cry a lot of times while buckled in. She used to move her chest clip down but she learned we would just pull over and wait until she put it back so luckily she stopped that.

She also tends to be aggressive. There have been a couple of times we had to move her twin out of their room for a few nights because she would hit/bite her sister after we put them to bed. There are also times she just randomly hits us or her sisters without being provoked.

She is also terrified of dogs and birds. If one comes anywhere near her, she screams and finds someone to hold her.

She is obsessed with everyone else's pee and poop, but refuses to sit on a potty.

She's very intelligent in some ways. She sees clues and asks questions - example I pick up my keys or put shoes on and she asks if I'm going shopping. Or she'll put her shoes on the wrong feet (on purpose) and say "look! Wrong feet!" Her vocabulary seems appropriate for her age. But she can only count to 5 and she doesn't know her colors. She knows all the colors names but doesn't identify them up correctly.

She's very social, no issues with eye contact. Loves hugs and kisses. She's good at creative play too.

Should I be concerned? If so, what do we do now?