Hard lumps inside the breasts in pregnancy are considered to be caused by the following conditions: First, it may be due to breast enlargement after pregnancy due to excessive secretion of estrogen in pregnant women, and the main symptoms include hard lumps inside the breasts, which can be painful to touch. Secondly, it could be mastitis, which will have hard lumps and pain in the breast, plus obvious redness and swelling. Then, there is the possibility of breast fibroids, the typical symptom of this disease is also hard lumps inside the breast. In addition to the above-mentioned conditions, it can also be caused by other breast diseases such as breast cancer. To sum up, whether you are pregnant or not, hard lumps in your breasts are abnormal. It is recommended to go to a hospital breast specialist for further examination, and after a clear diagnosis, further treatment will be done according to the results.