Hi Cazza
We had this exact problem. I think it is partly a developmental thing as they seem much more 'aware' of their surroundings and so can't switch off so easily at this age.
What time is her bedtime at the moment? We took a while to cotton on that we were keeping her up too long and moved bedtime forward from 10pm, to 8pm and then eventually to 6.30pm ish, by replicating the 10pm routine (darkend room and feeding her in our bed until she was dropping off and then putting in her moses basket). We made the room dark with blackout curtains, which helped her settle down if she did wake up. We did have to leave her to cry for a couple of nights, as she wouldn't be cuddled or fed when really overtired (due to lack of daytime naps) - it just made her scream more . This was on the advice of our hv and wasn't easy, but we felt that us trying to comfort her was actually just keeping her awake longer and making things worse. She cried for 40 mins the first night, 30 the second night and then anything from 5 to 25 mins over the next week or so. Once she was settling ok, I could feed her in the bedroom and then put her down after that.
For the daytime naps, initially, I just did what I had to to try and get her to get enough daytime sleep (its still an ongoing problem some days to be honest). Taking her out in the buggy, putting her for a nap in the swing even the car occassionally, but once we had got her to settle herself in the moses basket in the evening, (this was about 3 weeks after we moved her bedtime), I tried it for the first nap of the day, and although it took perhaps 15 minutes of grizzling, she did settle and sleep for 45 minutes. I then tried for her lunchtime nap too, which also worked. I have kept her in the buggy for her afternoon nap though, as I don't want her to loose the knack of sleeping in it if we are out and about. I put her in the dining room with a hairdryer on and joggle the buggy until she drops off (sort of replicates a walk iyswim).
I also found trying to pick up on her sleep signals (eye and ear rubbing and yawning) and getting her down for a nap asap once these started helped.
Sorry if this all sounds a bit garbled - it was trial and error to a degree and she still generally only naps for 45 mins at a stretch, so needs 4 naps per day, but things have improved, she has learnt to settle herself to sleep and she is a very, very happy little thing .