Hello Teen,
Hope you don't mind me sticking my nose in (so to speak!). Your Movicol should do the trick - just take more of it. I take one sachet daily to prevent constipation (I had lots of surgery on my bottom recently) and it works really well. If I feel myself getting bunged up, I take more sachets. On the packaging it says you can take up to 8 sachets a day for bad cases but you need to take them within a certain time frame (?6 hours).
If that fails, you need to go get an enema. If a small microlax one fails, a phosphate enema should do the trick.
Once you've dropped (!) you need to work on not letting it happen again. That is where the dietary advice comes in. Apricots, linseeds, fibre, good hydration and a daily movicol for a while. Are you taking any painkillers? Co-codamol/co-dyramol and tramadol can make you badly constipated.
Hope you lighten your load soon!
Hope that helps xx