I noticed that since I started loosing weight and exercising, that the back of my arms (where my triceps is) looks even more flabby..Am I doing something wrong ? My biceps looks kinda good though.

Sometimes your skin tone will look worse before it gets better.

Have you been doing exercises that will help develop the tricep muscle?

I do push-ups for my arms, I don't know if this works my triceps or biceps.

well it'd mostly work your biceps and chest. Although pushups are great, its hard to rely on one exercise to work your entire upper body.

I would do some tricep dips and look into things like tricep pushups (your hands are closer together to help work your triceps).

ok thanks a lot...i'll try that

Push ups don't work your biceps. Biceps are a 'pull' muscle that work with your back muscles in exercises like rowing and chin ups.

They work your pectoralis major (chest), triceps and anterior deltoids.

Good tricep exercises:
push downs on a cable machine
kick backs with a dumbbell
french press
dips on a bench - or sometimes gyms have machines for this.

Otherwise, an overall fat reduction would get the 'arm flab' down, since you can't spot reduce, only strengthen the muscle underneath.