I really didn't intend to do this but I did. I ran your height/weight/age on a standard calculator to determine the number of calories you should be taking in to maintain your current weight. I don't hold a great deal of stock in these calculators as they seem to run high in calories ... but it is a starting point to consider what it realistic.
According to the calculator, you need an average of 1700 to 1850 calories per day to maintain your weight. I'd bet an average of your weekly intake, considering the chips and ice cream comes out to about that level.
For perspective, I'm 44 years old (so we are about the same age)- 5'-9" and 160 lbs (but different body types). According to this site, I need 2100 calories to maintain my weight. According to conventional wisdom (which again, I don't hold a great deal of stock in but see as a starting point) I need to reduce my intake by 500 calories to loss a pound a week - essentially 1,600 calories. Currently I'm averaging about 1800 a day and basically maintaining my weight or maybe losing about 1 lb every other week. Right now, I'm essentially just starting living primal - on my second month (so take my thoughts with that in mind) - so I'm less worried about calories and more concerned about learning to eat this much without bread and chips which have been, honestly, a huge amount of my caloric intake before this. Along with that, I drink far too much wine and cocktails and that adds to the calorie load for me.
If you really have been taking in only 500 calories a day, I think your body is going to need to recover from essentially starvation rations. I'm betting you are actually eating more with the 'bad' food. A thing to keep in mind is that in reality the average intake over a week is far more important to look at than the daily intake.
Because I'm on a different time zone than you, I've finished my day and had dinner. I'd be happy to share what I've bought for the week and my thoughts/plans for the week if you are interested.