has my milk gone???

[agalch]

I am pg (due in July) and still bf my dd who is 20 months. She has been grizzly for a couple of weeks(been unwell)and cries when i tell her to come off the boob.She hasn't seemed happy after a suck and asks to go on again.I had managed to get her down to 3 feeds,1 in morning,1 in the afternoon and 1 before bed in preperation for baby arriving.She now wants it on demand again,i am saying no except for the 3 feed times.Thing is i don't feel like shes actually getting anything and i'm getting sore cos shes sucking really hard and on for ages.Could the milk be gone and what should i do now?Would have been more than happy to tandem feed but i don't know if i can have her chomping away for the next 4 months.