What Causes Uneven Endometrial Lining Of Uterus?

hi i am 29 yrs old today i had a scan and the doctor said that i have an uneven endometrial lining but my ovulation and everything is normal itseems and i have a regular 28 day cycle however my last period was very short and lasted for 1 and half day we are ttc and i am really concerned i already have a kid ,she was also underweight when she was born