LYMPH NODE SWELLING IN LEFT SIDE NECK MORE THAN THREE MONTHS

My age is 20 years i am suffering from lymph node swelling in left side neck  more than 3 months i have done all the tests like CBC , FANC, BIOPSY, CT - SCAN, CHEST X-RAY , TUBERCULIN TEST ALSO DONE and all  reports are normal i have taken antibiobiotics like oflin , doxycyclin , roxid, combiflam for pain but no result found my doctors says its just an infection but its  last for more than three months i am very worried about it that is it not a cancer like lymphoma or anyanything  else which is very serious becasue some time my lymphnode swelling become small like 1 to 2 cm. and sometime it become more 5 to 8 cm. please tell me what to do immediately .
for your information i first noticed my lymphnode swelljng 25.07.2011 at evening 4 Oclock.suddenly i am sure before that i have not this swelling and my doctor do this  when swelling increases inject a injection in it and take out the pus or yellow colour water from the lymph node and swelling reduced but after 1 week it comes again . i think 4 to 5 times he do this .

[Caryopteris]

Do you have any tooth discomfort?  Maybe you have an oral infection like an abscess.  Any infection of the head or neck might cause this.