5 days into cycle uterine lining meaasured 7mm already had hysteroscopy which showed mildly proliferative but is 7mm too thick?

No. 7mm would likely be consistent with the endometrium specimen that shows mild proliferative. Proliferative just means the lining is getting prepared for ovulation. In general once the lining gets over 15mm in thickness then we start worrying about the possibility of hyperplasia. If overly concerned consider getting an endometrial ablation. I prefer Novasure. That should end all bleeding issues.