Breastfeeding

Hi my baby is 6 weeks old and is breast fed I feel she isn’t getting enough tho she seems hungry after every feed I put her back on and she just thrash’s and pops back off. Any recommendations on how to build up milk production? She weighed 3.8kg at birth and in first 4 weeks went to 4.25kg hasn’t really put much more weight on tho was 4.4kg 2 weeks ago then 4.5kg on Monday. She is also had to get on she thrash’s around before attaching. Any tips would be greatly appreciated 😊