Your immune system is definitely in need of good nutrition, proper vitamins, rest and exercise.
Start a good, well balanced diet, add the vitamins: C, B, D, and A, also add a good, multi mineral as well.
Exercise at least 35 minutes a day, I like brisk walking.
Stop the smoking and alcohol, drink lots of water and fruit juices.
If possible, do some research on "de-tox" and try that as well.
Well, it sounds as if your immunity is low.
Being overweight and out of shape is not good for your health, but I'm sure you know that.
Alcohol harms the immune system, as does smoking. Are you smoking pot? Some studies have shown marijuana decreases white blood cell counts (which is the basis for your immune system.)
I think if you re-read your post, the answer is right there. Start taking better care of your body! Try to lose weight, don't drink booze, and stop smoking.
Eat a well balanced diet; no junk food, soda, chips, candy, etc. Lots of lean protein (fish, poultry) tons of veggies, fruits, and drink a TON of water.
We only get one body so it pays to care for it...being sick sux...Good luck.