Oo normal yan, mama! At 30 weeks ang baby mo ay lumalaki na talaga kaya parang rock hard ang belly mo sometimes, lalo na kapag active ang bebe or pagod ka na. A few of us pregnant mums actually experience that rin, sometimes it's just Braxton Hicks contractions (practice contractions) which ay totally normal, pero if matigas talaga most of the time or may pain, better check with your OB lang para ma-assure ka na everything's okay with baby at sa inyo. Congrats sa pregnancy!