Although your new partner is likely to be clean as he says, still, since you developed the symptoms after being with him, you should get yourself tested for STD's.
A number of STD's, specially chlamydia, could cause this. Hence this must be ruled out. You should consult your family physician, or preferably a gynaecologist, for this.
If it is not an STD, this could be Bacterial vaginosis, which might also cause similar symptoms. Your doctor will be able to tell you whether this is the cause.
The bump could be a lymph node which has swollen due to infection. The presence of the bump, if it is a recent one, is apointer towards STD.
The swelling could also be a Bartholin cyst. Your gynae will be able to diagnose this also.
You should look up these links:
http://www.mayoclinic.com/health/bartholin-cyst/DS00667
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