Got stung by a bee on my shoulder yesterday, today got swollen lymph node occuring in armpit, is this normal reaction? if so when should swelling go?

Bee sting : It looks like you don't have systemic reactions to bee sting since you don't mention that you have problems breathing, throat closing, abodominal pain, nausea and vomitting. A local swelling at sting site can associate with local lymph nodes swelling and does not need specific treatment. It would last a few days to a week or two. If the swelling is large and causing pain, you should see a doctor.

Normal response: Lymphatic system absorbs/carries things too big to go into the arteries/veins like bacteria eaten by white cells and digested food. Lymph nodes "taste" the lymph for anything bad like bacteria/viruses/cancers, etc. When it detects a problem, it alerts the immune system and your body reacts. They enlarge in response to the inflammation they create when they react. They shrink when all is well.