bowel habits have changed. I have become constipated

My bowel habits have recently changed. Previously I would make a bowel movement about 2-3 hours everytime after eating, they would be easy to pass, and usually soft, or sometimes shapeless/bordering on diarrhoea.

The past 2 weeks I have become constipated, my bowels are weird shaped - it's like the one stool will be big then thin then big then thing and so on, like they're wavy. They're also pale and hard, and I cannot completely empty my bowels in one bathroom trip, I always feel incomplete and like I still need to go. They've become pale and they smell unusually foul.
Sometimes, there will be a clear stringy type membrane attached to the end of the a stool, or a lot of greasy type goo will come out at the end.
I also get waves of nausea throughout the day.

I went to the Dr and she said not to worry, just to eat more fibre, but I already eat plenty of fibre and I haven't had any dietary changes.

Should I get a second opinion?