Consult your GP and then a nutritionist/dietician depending on what the GP said.
Ultimately based on what you have said I don't think anyone can give you a proper answer.
However if it's not a medical issue then....you say you are in a calorie deficit with 1600. That should roughly mean if you eat 2100 calories a day you'll maintain your weight (age/sex may change that). If your maintanence weight is higher than 2100 then you're not eating enough probably. How long did it take you to lose those 9kg? It should have taken longer than 9 weeks. Generally speaking if you lost it quicker than that then you may be risking your health, it's also not sustainable. Remember, if you're on a deficit, by it's very nature, you should be hungry. If I've got that wrong then up your calories by 250. You will still lose weight, at a slower rate, but may feel less hungry.
The type of food you eat also matters. 1600 calories is around 7 mars bar. If that is all you have all day you will be starving. A good balance of protein, fat, fibre and carbs. If you don't already have a healthy diet then it may take a while for your body to get used to it and feel hungry.
Instead of crisps , keep some chopped celery/carrots etc and some low fat fromage frais or something around to dip them in when you get hungry.