Can You Eat Fast Food And Still Lose Weight?

In the past few weeks I seemed to pick up a couple of extra pounds.  I'm working out and watching what I eat and still gained weight.  Maybe I'm not working out hard enough or could it be the fast food breakfast in the morning.  In my mind it can't be the fast food, because the portions are so small they don't even fill me up.  I read that it contains high fat, starch and salt which contributes to weight gain.  In light of this new information I'm going to change the way I eat, so from now on I'm only ordering from the dollar menu.  It's cheaper.....got to be less weight.