Gud eve! Oo naman, normal lang mag-experience ng belly pain during pregnancy, especially ngayon na 4 months ka na, ang ligaments mo ay nag-stretch pa lang and your uterus is growing, kaya may pulling or cramping sensations talaga. A few of my mum friends had the same thing around that time, so hindi ka nag-iisa sa experience na yan. That said, kung ang sakit mo ay severe, may spotting, or hindi lang dull cramping, best pa rin na i-check mo with your OB para ma-rule out kung may ibang cause at maging sure na lahat ay okay with baby. Better safe than sorry, especially pag first pregnancy mo pa yan!