Feeling a heartbeat/pulsing sensation lower stomach/upper pelvis week 4 and a half.

My hcg raised slowly (24%) over 48 hours recently. I have felt a throbbing pain in my side for a couple hours today but then a bad pulse/heart beat sensation below my bellybutton upper pelvic area then accompanied by overall stomach cramps and lower back pain (below ribs to pelvic bone). Looking online I see nothing about a pulsing sensation in that area this early in pregnancy but it's good in the second or third. Anyone have advice? Very weird feeling. The pain was horrible for a bit but then took a hot bath and it's not as bad now.