How is she doing today?
Sounds like she's getting close. Probably less than a week.
Sometimes my sheep go into false labour a time or two prior to actually popping out lambs.
Or possibly, if she's especially wide she may just be having trouble with the youngins taking up too much space and not leaving
enough for her lungs and rumen. If this is the case, she is probably eating smaller meals, more frequently and may not want normal grain as it can cause extra gas in the rumen. It may help to have free access baking soda to reduce the gas buildup in the rumen.
IF (and I know it's a big IF with sheep) you can get to her without stressing her or you out, you can feel the muscles above the tail. Sheep seem to relax that muscle group as they prepare for their 'hatch day' - like goats do. It's harder to feel it if they still have their wool on, and I've noticed in my flock it can be anywhere from 3 hours to a week from when they relax those muscles to when the lambs pop out.
What kind of sheep? What are you feeding her? What kind of grain(s)? What minerals do you give them? What is the Selenium like in your area? Se has a huge effect on sheep and goats especially during pregnancy and lactation. Another issue could be a mineral imbalance.
It's hard to know if there is something wrong, or this is just how she's going to be this year. Going off the grain is definitely a sign to watch her closely, but may just mean she's very close to popping out lambs. Or it could mean you opened a new bag of grain this week. Is she eating her normal feed/pasture/hay? Is she drinking? How's her waste management system?
Looking forward to photos of little lambs.