> It has nothing to do with the site of injection
> It also has nothing to do with smoking
. Tobacco only adds more problems.
Congratulations for quitting the smoking - you deserve to be appreciated for the motivation and achievement. Keep it up.
> The reaction this time could be due to other reasons
- Changing the brand / the solvent used might have been different, even though the drug is the same
- Infection / at the site of injection or the instruments
Antihistamines and local fomentations could help
Try to see your doctor again - if you feel you need further assessment and assistance