Oo normal yan, mommy! Yung tigas na parang rock tapos mawawala, that's likely Braxton Hicks contractions na nagstart na sa second trimester, lalo na kung regular time sya nangyayari like your afternoon. A few of us moms experienced the same thing at around that timeframe, at mawala lang talaga after a few minutes or when we change position or drink water. That said, kung bothered ka or gusto mo sure, better to check with your OB lang para peace of mind, especially if may cramping or spotting na kasama, wala naman dapat ikabahala pero it's good to confirm para relaxed ka throughout your pregnancy! Enjoy your second trimester, mama!