Why can't our Sick Sims go to the hospital?

Exactly the medicine work for awhile than back to being sick again or sometimes the medicine option don't show up on the computer on some houses the pregnant Sims get a chance to go to hospital and have baby why can sick Sims go like they children can stay at home call in sick go to hospital and get checked out and the doctor either give a shot or medicine and they feel better or give them a day or two to rest at home before doing activities.