Okay so i dont know what this is or if its normal and i have no one to ask as they all get annoyed cause im skinny so i should shut up ext

So im average i guess more on the skinnier side, but recently in the last month ive gained weight but only in the stomach an uterus area an no where else it looks like ive swallowed a balloon (smaller bit at top an bigger bit down) its painful if i push on it an its a bit hard ?? i dont know if this is normal ive never had this before i dont know if its just poor exercise (which ill remedy soon with the gym) or if there is something wrong with me ???