swelling

my 5 month old son has today just got swelling on the back/right side of his head(possibly a funny shaped egg shape- hard to explain) it is overly large. i took him to the docs today she said to keep an eye on it and when took to HV get his head circumfrence done n keep check on it. i did so. and it was 44 , however when he last had that done which was a couple of weeks ago it was only 34. the HV said that is alot to go up by. i am genuinely worried n i no doc said not to, but i am. any ideas? what it  could poss be ? or what to do ? as cnt just walk in a n e as surely they nt class it as a emergency.i live in nottingham main hospital to me is QMC. i have a 17 month old daughter too av never had any problems like this before.

[AnnieBrooke]

I'd ask for another doctor appointment and point out to the doctor who ordered the circumference to be measured that it has gone up from 34 to 44 in just two weeks.