LO keeps pulling off. Any ideas?

[Tulip2013]

My 3.5mo has always struggled with BF and finally had PTT diagnosed and dealt with at 8 weeks. She has much better since but in the last week has been pulling on my nipples and grunting / squealing and coming off every few minutes. She is slow feeder (1hour) but this behaviour means it's taking even longer than usual. Sometimes she just comes off and looks at me for a couple of minutes - cute but I want her to keep eating.

Any thoughts why and what I can do?

I remember my ds doing this when he got to an easily distracted age. A nursing necklace for him to fiddle with when feeding helped.
But then it could be something completely different

Things that sometimes work for me:

1. Burp the baby and put back on
2. If still coming off offer different side
3. If still not working take a break and try again later.

My 16 week old is like this all of a sudden. It often means she needs a burp, or that she's finished. We have days where she has lots of short feeds rather than a few long ones. I read somewhere that your milk changes around this age to respond to their changing needs.