How can I make my puppy trust me?

She is 8 weeks old. I train her with treats and affection. But she is also in trouble alot for 'puppy stuff'. I am not sure if she is scared of me or not.... perhaps I get her in trouble too much or too harshly. When I go to pick her up, she will duck to the ground a little big and step back! I don't know if this is fear though because of her reaction to other dogs. When she meets other dogs, she will approach them, but put her tail between her legs, and duck as close to the ground as she can. She will approach their front legs and almost seem scared... but she is the one approaching them, so she must just be submissive or sensitive. She is confident in most situations and happy go lucky. Is she scared of me or being overly submissive? (she started all this behavior at about 6 weeks old... we got her at 4 weeks old when her mother died:( She is not like this with my older dog though, so why with me? Is she scared of me? I am strict with my kids and pets but also very loving.