I really feel for you, especially because picking up the toddler isn't easy and isn't something you can NOT do. I have a five year old and thank goodness, she doesn't require picking up anymore.

Please be wary of not creating a bilateral situation since you could be favoring your good side. I don't have any advice for you other than try to not do do everything one handed and/or modify how you do things. I'm bilateral and it's no fun trying to choose which arm gets to take a beating. How is your head posture, is it forward or tilted up and back? Try to lengthen your neck by imagining a string is attached at the crown of your head and you are pulling it up. I know, this is silly but it's a good visual that I learned through the Alexander Technique (Google it for more info).

Is the numbness and pain constant or does it come and go? If it's intermittent, try to document when it occurs and/or what triggers it. Is your PT also doing massage of your pecs (minor and major)? If not, ask them about it because a lot of TOSers have pec issues as well.

You've definitely come to the right place, there's a lot of info on these boards. Good luck.