Baby poop - any ideas?

[Bumbleconfusus]

I know this should probably go in health, but I thought I might get more help here...

My 18 week old DD has had an upset tummy for almost 4 weeks now, she does anywhere between 2 and 6 (so far today) dirty nappies. She is BF. From when she was about 6-14 weeks, she had what I would consider normal BF baby poop ie- thickish yellowy and once or twice a week. Then suddenly 4 weeks ago on Tuesday, she started getting diarrhoea... but I don't know why and I don't know ho to make her better.
I had nipple thrush so I used the cream for about 4 weeks (started sing it about 3 weeks prior to the onset of the upset tummy) but have since stopped using it in a hope that it night help the upset tummy. I am not giving her anything other than BM now, no gripe water, no cooled boiling water, I'm using no nipple creams or anything. She is now being bottle fed 3 days a week (with defrosted EBM), but I sterilise everything, and she only had that for a week and a half (so had the upset tummy a couple of weeks before I started doing this).
The dirty nappies are not only frequent but extremely runny, and fluctuate between green but generally yellow, sometimes slightly seedy but not like they used to be. Also sometimes foamy which I've read can be a sign of only getting foremilk, but I am extremely careful with getting her to finish a side before she starts the next.
The HV knows and I've taken her to the doctor who doesn't think its an infection, she's not losing weight and hanging onto her percentile (2nd), their response is just to weigh her more, and to be fair I don't know what else they could do.

Does anyone have any experience, advice, ideas about this?

All I know is that when she was about 5 weeks my DD started to have green foamy, sometimes bloody, nappies out of the blue. Her poo was tested and infection ruled out and she was fine other than the poos. Then, after maybe 4 weeks or so it just all went back to normal.
We had both had thrush and I suspect that her gassy tummy from the yeast was making her poos green and the force with which they were coming out explained the blood. She had nystatin for thrush which didn't seem to work but after we finished the course her mouth seemed to clear up by itself. Do you think your baby might have thrush? Have you checked her mouth for white patches? Do her poos smell yeasty?

she has no signs in her mouth, her poos don't really have much smell, just sweet, though sometimes remind me slightly of banana? I have a script for the gel for her, but didn't want to use it incase it made things worse

From day one my LO has been pooing up to 5 or 6 times a day..She always cries when it happens too. Went to the Doctor and got a home visit from the HV and they said it was normal for a breast fed baby. Sounds like your LO is going as frequently as mine and mine is well and gaining weight. It is worrying though I know but I hope your DD is just going through another change in her digestive system. Hope all goes well

Bumble, my friends DD had almost exactly this. (in fact i had to read several times to make sure it wasn't her!), probably about the same age too. Started going up to 6 times a day, very green! Over the weeks it got less and less until cleared up, but it did take some weeks. She took a sample to the doctor which came back clear. No idea why it took so long to clear up. Baby continued to gain weight throughout, albeit very slow. I guess just let the doctor know how long it continues for incase they want to check a sample. Hope she clears up soon.

thank you very much for your replies, it is a relief that it sounds similar to some of the experiences you (or your friends) have had. I guess I will just keep trying to wait it out, but its good to know there could be light at the end of the (poo covered) tunnel.