I still have not been able to win 6 star or multiplier prizes in a row to win those achievement trophies. Any suggestions?

Lynelle is correct, and of course, make sure you are playing on a stage where you have won all your prizes and remember to max out your collections as well. Also, make sure you stay away from the game eggs and the eggs that give more than 1 prize, because it usually doesn't have 2 of the same thing. Also, once you have cracked several eggs on the screen and get either stars or multipliers (whichever you are going for), refresh the screen. That way there is a better chance that there are more of the items that you are looking for.