Teeth white problems?

Ok so I just recently asked my dentist about tartar and he said that I might just have brushing problems. My teeth aren't as white as I see everyone elses and I feel really uncomfortable now because I want my teeth whiter, he said that I probably have just been brushing them wrong, I have of course your supposed to brush with a 45 degree angle down dowager the gums and I've been brushing head on. He suggested a automatic toobrush to help get the plaque off easier and I bought one. I've been brushing for about a week now and my teeth have been kind of better but still not that white. My question is, will they get even whiter? Do I have to brush for longer to notice changes? What are some of your tips? I brush every morning and night, should I brush 3 times a day and will that make a difference?