I agree with Fiona. Sounds like you are so sleep deprived that it is now affecting your ability to function normally. Also, agree with the possible reflux - could even be silent reflux where bubs doesn't actually spit up anything but the milk & acid rise up then they swallow it again - it burns coming up & going down, so bubs would be in pain. Elevating the cot can help alot & also keeping them more upright for longer periods, even after burping may help. My gf used to put her son in the rocker for a bit - slightly elevated and once he was old enough in a walker type thing.
To elevate the cot you can do two things - bricks under the legs of the head end or rolled up towel under the matress & base.
When your mum is over can you ask her to help prepare something to eat for you - just b/c it isn't 12pm doesn't mean you can't eat a sandwich like Fiona suggested. Meals don't have to be at certain times, just when you are hungry or get a chance.