bf baby not gaining weight

Ashley
Well I have to make a decision... My daughter is not gaining weight... She's down to 7 lbs. (that's 3.5 oz this past week & a total loss of 10 oz. in 2 weeks 😢)... We go back Tuesday at 3 weeks for another weight check...
We already use a shield due to my slight inversion and her being born tongue tied (was clipped in the hospital)...
So I have 4 options to decide on attempting...
 According to her doctor (he is supportive on keeping to the breast if it works)...
1. Pump to supplement 
2. Pump exclusively
3. Supplement formula
4. Switch to formula
Trying option 1 first...
Either way we have to start measuring more of her intake to know better what she's getting... Anybody with any ideas or advice??? I don't want to give up yet...