Backup size keeps increasing without finishing

So, my WhatsApp stopped backing up on March 23rd. I tried to do it several times but failed. I had about 2.1GB to backup. I think it's because there was no space in Google Drive. I saw that Google stopped giving free storage for WhatsApp backup and I had the normal 15 GB Google Drive. My backup is 19GB. So I purchased 100GB Google Drive. Then I clicked backup and it said 700MB to backup. I thought it was weird. So anyhow I clicked backup but it got stuck at 99%. Then I cancelled and clicked backup again. Then the size became 800, the same thing happened; getting stuck at 99% so I kept cancelling and restarting and every time the storage increased by about 100MB. Right now I'm backing up for like the 15th time and it's 2.8GB. What's happening? Will I have to keep doing this until it becomes 19GB?

Also I deleted about 3GB of media from a chat, could that have done something to the backup? And is it trying to back everything up from the beginning until now?

Please help.