You are unlikely to have lymph node enlargement due to herpes in the absence of overt herpes skin lesions. Lymph node swelling in the groin is very common, often due to unnoticed inflammatory lesions of the leg, foot, etc (even a stubbed toe can do it); so it is likely that symptom is coincidental, not directly related to your recent sexual expsoure. Also, not many 16 year olds have genital herpes, so you partner wasn't infected. (One of the uncertainties about herpes is why it is so much more common in older sexually active persons. Whereas the highest risks for gonorrhea and chlamydia occur at age 15-25, HSV-2 infections most commonly are acquired at age 25-35.)
So I'm not so sure you need a herpes blood test. But if you decide to do it, wait until at least 6 weeks pass. In the meantime, if the lymph node enlargement resolves, don't worry too much; but of course if it continues or worsens, see a health care provider.
Good luck-- HHH, MD
He's not 16. He's 21 and stated that he had the exposure 16 days ago. Just FYI.
Also, just to clarify, you are saying that most of the time that people have swollen lymph nodes due to herpes it's accompanied by a physical (lesion-based) outbreak? That's reassuring information. Thanks.
In 30+ years in this business, I have never seen a case of inguinal (groin) lymph gland enlargement, without genital lesions, that turned out to be herpes. But I can't say it never happens.
HHH, MD
thanks