Hi,
Welcome to the ehealthforum. I am glad to help you out.
Itâs very difficult to comment regarding the nature of the lump without a physical examination. However, the few differentials which need to entertained are
1) it could a benign tumor of the uterus called fibroid which has now become palpable due to the pregnancy.
2) It could be an ectopic pregnancy (pregnancy in the fallopian tubes instead of the uterus).
3) It could be a mass due to a loaded colon if you are suffering from constipation. The best & safe test to find the cause of the same is an ultrasound of the abdomen which I suggest you to get it done at the earliest.
Please do consult your obstetrician for the same. I sincerely hope that helps. Take care.