I had one.
It came up at the end of the 2nd tri for me, was worried sick and my doctor was really unreassuring.
In the end I went to see a private doctor and it was a lymph node, well 2 swollen together. They said leave it alone and it should go, if was still there after baby to go back.
I then had one swell up under my tongue - I didn't know it was a lymph node til after I had the baby and went to the hospital (i'd seen my dentist at first and he had no clue what it was!). This one came up not long after the armpit lump.
I guessed that it was hormones playing up.
After having Oscar they didn't go down for aaaaaaaages. I then had one come up in my chin and one in my groin recently.
I read somewhere that if you leave them alone for six weeks they go down... well them have all gone down now (my LO is now 8 months and the first lump came up over a year ago!) Anyways, the only one I still have is under my tongue, I can't leave that alone coz I like to eat lol
Sorry for the blah, but basically I think some of us are susceptible to lymph nodes swelling during pregnancy due to hormones, Think mine still went mental after the birth because i was breastfeeding!
xxxxx