Hard drive storage issue

Hi guys! I've been a professional photographer for less than a year and usually keep anywhere from 7-12,000 photos in Lightroom at a time, with no issues. About 48 hours ago, I tried to import my photos I took from a day of 5 shoots, and Lightroom said I needed more hard drive space. I deleted 6,000 photos off of Lightroom and stored everything on an external hard drive, but I'm still unable to export or input anything because of this storage issue. Does anyone know if I'm doing something wrong or if this is an apple issue? Thanks so much!