Well, ah, keep in mind that all pokémon are oviparous, meaning they lay eggs. In other words, it’s highly unlikely that your mamoswine is actually pregnant because, well, mamoswine can’t actually get pregnant.
It’s likely that she may be sick, dealing with a vitamin deficiency of some sort, struggling with a mental health issue, or had actually laid a clutch recently. First, check her habitat for any sign of eggs. If you don’t see any eggs, take her to a pokémon center as soon as possible and have her examined by a Nurse Joy. Your local Nurse Joy should be able to spot what might be causing these odd behaviors and suggest possible courses of action.
Best of luck, anonymous!
The Pokédex According to Bill 