I do cardio 3 times a week... But, I still got lose arm and armpit. My breast is quite big but loose.

My weight and weight within normal BMI. Even the lower side.

you can try doing push up and triceps dip. push up good for upper body and chest

How to tighten loose skin while losing weight
Well from what I understood is that fat gone from underneath skin will form loose skin if the weight lost happens fast b4 the skin got time to contract back.
If it is very drastic then might have to do surgery.
Otherwise build up muscles around the arm to have the muscle bloat up to "replace" the fat lost.

Like the above, but be aware that muscle mass is more dense than fat.

So dont worry if you gain some weight even when you're working out, Its muscle replacing the fat. But usually its simply no/minimal weight change.

Even i m gal, I need to do weight?

yes. to have lean body

try doing more push ups / pull ups to tone up your arm region?