I agree it is all nap-related as everyone else has suggested.
I have 4 dcs, the youngest is 23 months, so I am currently going through this at the moment. With all my dcs they dropped their nap at around 2, dd3 was about 2.5 yrs. it's a frustrating time. I found shortening the nap not particularly useful as they still wanted that longer nap sleep cycle. Meant they were very cross when they were woken up.
I don't think there is any effective solution, you need to work through the next few months to find out what routine works for you and your dc. I understand the struggles of being pregnant as I had my 4 dds in 5.2 years.
Some things I would try is napping earlier (that helps for a short while), napping in the buggy to encourage shorter sleeps. I find that they usually sleep less 'soundly' when out and about and tend to not wake cranky. Waking up to a favourite tv programme (not a huge fan on tv, but I am a fan of happy babies). Transitioning is not instant and it takes a while to sort out what suits you.
My dds have all been very restless sleepers. Dd4 talks a lot in her sleep also. She is an earlier riser, but I am currently trying to get her back to sleep at 5:30am by breastfeeding so she will wake about 7 and then skip her nap and go to sleep quickly inthe evening. If she wakes earlier, I'll try to feed her or walk her i buggy around 11am so she has a shorter nap. There is no hard and fast solution.
Finally, as someone said above, being relaxed about it will really help. I wish I had known this, I've adapted to the crappy sleep I get. I see my oldest dcs as amazing sleepers now at 7 and 5yo and know they'll all sleep like that eventually. I know it is hard not to stress about it, ESP when pregnant, but their sleeping patterns to change. Perhaps really trying to wear her out during the day: scooters, soft play, park? May help.
Best thing is when she finally drops the nap, she will probably be falling asleep before her head touches the pillow!