Had blood taken which caused bad bruising. 2 days later have painful lymph node under same arm, feel otherwise healthy. Do you think its infected?

Skin infection. When there is a break of skin such as taking blood bacterias live on the skin naturally moves in and gives you all the troubles that you are experiencing including the lymphnode under the same arm . Call your doctor and get some antibiotic. Check this link. http://www.nlm.nih.gov/medlineplus/ency/article/000855.htm.
Unlikely. but certainly possible... Apply heat to swollen area and consult a Medical Professional as soon as possible. On the off-chance this is an infection antibiotics may be necessary! Hope this helps Dr Z.