2-3 days ago I was bitten by a bull ant and ofcourse it stung\hurt a little bit. Now, its really irritating and very itchy, there is also a lump.?

Fire ant. A local reaction to a bite may last for up to a week. As long as you are not sick in any other way and there is only red color at the bite site treat the symptoms. Any doubts see your doctor. They are nasty. All the best.
Allergic vs normal. Under conditions you listed chest pain/chest tightness if this is since the ant bite you may be having a serious allergic reaction and need to go the the hospital as soon as possible. An ant bite can normally cause all the signs you described. Local treatment can include over the counter steroid creams, peroxide, topical antibiotic creams.