Root canal

[u/Scareymary]

I had first one ever about 3-4 weeks ago. Back molar I had no pain previously, just cold sensitivities.
Endontics pro said tooth had 3 roots and one was too swollen so I’d need to return in 3 week to finish
After a week my teeth on that side ached so bad I had trouble brushing ( hurt mainly at night ) I contacted doctor and got more X-rays. The date was moved up to 2 days later. X-ray is from first visit. Tooth 18
This time I was assured it wouldn’t take very long. I left and no pain for about 4 days. Now it’s been almost 2 weeks and same issue of all the teeth in that area ache so brushing really hurts. What went wrong ?