My 4 month old seems to go from happy/smiley to screaming in anger within a split second... he's so temperamental! Can babies this age have "tantrums"? Should I be worried about his anger? This is different to him letting us know he's hungry/tired... it's more screaming out of boredom / frustration... he doesn't seem to stay entertained by anything we do with him for very long, then let's us know about it! Is this normal?!