Yes it sounds like sciatica. Mine gets aggravated when I sit on a hard floor or sit down for too long. Try to keep a good posture when sitting and keep active. Definitely see a doctor as they can suggest exercises for you to do.
go see your gp. i have been in agony at night for last couple of week and im only 24 wks. didnt expect to be getting any pains for another couple of mths. gp was lovely, straight away said 'we need to get you referred to an ob physio now.' in meantime, get yourself a hockeyball and sit on it (put it on floor under one glute) and roll around on it. i do this anyway for trigger point therapy myself. it will hurt at first then after a few mins should give you some relief. hth
Not slumping on the sofa helped, as I'd been doing alot of that. Raising knees up to rock up from lying position also really helped. Someone recommended a girdle support or tuby grip kind of thing from the nhs physio.