17 weeks with twins

Iam Having twins.. But any other mommys feel like there having triplets?? Is that even possible?? Like one could be hiding right? There's just no room to even eat or breath in there for me.. I have to sleep sitting straight up at night! Other wise I feel pressure in my head and behind my eyes but my O2 levels have been 100%.. Ive already gained 24 lbs! The twins are in my lower front but i feel like theres always something putting presure in my upper right side by my rib cage..