I’m 4 months postpartum with first baby and have joint pain?

Hi I’m 4 months post partum with first baby and have joint pain++ I’m eating pain killers. It’s worse in the morning, every joint seems stiff and sore and particularly my hands and ankles and they are swollen I’m morning. I have to crawl to the bathroom then it eases up
During the day apart from if I sit for long. My fingers and ankles seem the worse and lower back. I’m so fed up not with this. I went to gp they have tested me for rheumatoid arthritis, lupus, and autoimmune diseases and all came back normal. I also had my thyroid tested, liver and kidneys. The only thing that flagged up was my kidney function which was poor so got it repeated and was back to normal. The doctor said it had likely been affected by anti inflammatory med he put me on so he has stopped that now. All I’m taking is co codamol and trying to get on with it but it’s ridiculous I feel like a 90years old. The gp doesn’t want to no now and thinks I’m exaggerating. I’m not over weight apart from some baby weight I have put on. I was very healthy and fit before getting pregnant and now after having my baby I feel terrible
Physically. I go to classes with other mums and no one seems to know anything about this and they all say they are feeling fine. The doctor has said maybe I just need exercise but I can hardly move never mind exercising! I was quite fit before having my baby and exercised regularly now I just can hardly bend up and down!
During the pregnancy I did swell up quite bad with fluid but that went away a few days after delivery. In fact I didn’t feel that bad immediately after. Please help

Age: 31
Medications: Co codomol
General Information: Yes and had several bloods which have all came back normal