Jumping up and biting - help

Bailey is for the most a really calm dog especially if she gets her daily walks (two walks and we are usually gone for an hour each time). But on our walks she's a little difficult, first she doesn't want to walk and stands still every 2-4 steps and I try to convice her to keep walking, then finally after 20 minutes or so she walks steadily but keeps eating everything interesting to her on the ground (I am always with my son in the stroller on the walks).

Now and then she wants to attack me and jumps on me and bites holes in my t-shirt, it usually always starts with her biting on the leash. I try to make her sit and calm down and most of the time it works fine and she will walk fine until the next attack.
Most of the time she attacks when we are on our way back and always on our street just a few houses before our home.

Today when we came in she run to the water and when I got my son in the living room (which is gated, I have to separate them most of the time) and walked back to the kitchen area she came running towards me and bit a hole in my son's sweater which I was holding at that time.

How can I stop these attacks... I must honestly say sometimes I am almost scared, especially the thought that she's still growing and will get bigger (she's now 30 pounds) I really want her to stop this behavior.

When I tell no bite in a firm voice she sometimes gets even nuttier. At home she usually doesn't jump and bite that much but goes after my feet and ancles, ignoring doesn't work and she will just keep biting until it hurts too much for me.

I can't really leave the room as she is without in the common living area, so I have a tie down or I put her in the crate for a few minutes (both in the same area).

Is this mouthing and jumping up still normal at 4 months?
Thanks for any advice.