At 30 weeks it's unlikely to be your mucus plug since that usually comes much later, but the jelly-like discharge mixed with the sensation you're describing is definitely worth checking with your PD just to be safe. A few of us mums have had random discharge changes during pregnancy that turned out to be nothing, but since you're noticing something different from your first pregnancy and feeling sensations near your rectum, better to get it confirmed so you have peace of mind. Your doctor can do a quick check and rule out anything that needs attention.