Ay, totally normal yan sa 5 months, mama! That hardness you're feeling is usually your uterus contracting, we call it Braxton Hicks contractions, parang practice contractions lang para sa big day, tapos talaga naman mawawala after a few seconds or minutes. A few of us pregnant mums din nag-experience nito, nakakascary muna pero totally harmless siya. Mas mag-increase pa yan as you get closer to delivery, pero just to be safe talaga, better mention it to your OB next visit para she can confirm it's just normal uterine activity at wala nang ibang concerns!