Uy, totally normal yan sa 28 weeks! Ang baby mo ay nagtutulak na talaga ng lungs mo pataas, kaya konti lang ang space para huminga, a few of us went through the same thing at yan ang panahon na super hirap talaga. Plus ang extra blood at fluid sa pregnancy, lahat nag-coconspire para maging mahirap mag-breathing, lalo na pagkatapos kumain o pag-akyat ng stairs Ang good news, it's your body just adapting, hindi yan sign na may problema. But since you have 2 kids na, I know you're juggling a lot, so take it easy when you can, sit down more, eat smaller meals, at try slow breathing exercises. Worth mentioning to your OB next visit though, especially if it gets worse or you feel lightheaded, just para may peace of mind ka!