So sorry to hear that you are still dealing with the pain this far after the trauma. While you do not mention any other symptoms except for the dull ache, and it is not clear if the ache is in your back or your chest, it would be important to discuss anything else with your physician, and also to discuss your aches if you continue to experience them for some time. The tackle itself sounds somewhat serious, and I would suggest that you visit a physician as well for a physical exam to make sure that there were no fractures or other smoldering injuries that might need more intervention than just 6 weeks of rest.
It is appropriate to discuss some things that might be wrong, however.
Your chest is extremely well designed to protect the vital organs within. The muscular and bony composition of your chest wall can cushion large amounts of force. The ribs all join with the sternum in cartilaginous joints that offer a small amount of movement when under extreme pressure. Forcing movement in those joints can sometimes result in pain and inflammation.
Alternatively, the deep muscles of your chest wall can bruise
like any other muscle, and will take time to heal. Over the counter non-steroidal anti-inflammatory drugs (NSAIDs like Ibuprofen) taken for a short period of time might be of some benefit, but please speak with your doctor
if your symptoms continue.