Physical limitations while pregnant

I am a very active and I consider myself to be a fairly strong person. I typically lift 50-60lbs on a daily basis with ease. When I had my son almost 4 years ago family members warned I might hurt the baby. I shouldn't lift my hands over my head, don't lift or carry ANYTHING,etc. etc.  and I listened not wanting to hurt my child but after I had him I felt weak and unhealthy. My job also requires some lifting. How much weight or activity should I be concerned with once I do get my bfp?