Context:
Naturally, used to get extremely heavy and painful/nauseating periods, which were reasonably long-lasting (4 days proper bleeding, couple of days tail-off), and came every 4 weeks-ish.
Then went on microgynon. Withdrawal bleeds still quite heavy, but nowhere near as painful as natural periods had been. Duration a little less than before (2-3 days proper bleed). However, often took pills continuously to avoid having any periods.
Implant:
0-3 Months:
I had a long period of continuous and then almost-continuous bleeding. But this was light, and not painful - a nuisance more than anything.
3-6 months:
Annoyed by semi-continuous bleeding - Took microgynon (in the normal way) in addition to the implant to have regular periods. These were as when I was just taking MG, but much lighter and not painful at all.
6-12 months:
Gradually weaned off the microgynon use. After this had v irregular bleeding about 50% of the time, extremely light and painless as before, with occassional more "proper" period like bleeding.
12 months onwards:
Irregular/continuous light bleeding gradually became less and less frequent, and more regular period-like bleeds began.
Periods are now quite normal-good: moderate flow, shorter duration (proper for around 3 days, then slight tail-off) actually hardly ever painful at all, slight discomfort. Actually come round less often than before, now every 5-6 weeks. Can be slightly unpredictable.
I'm 3 years in now, so about to get it replaced. It was (as you can see) rather a lot of bother, but I don't regret it, because even though periods were intially very irregular/continuous, even during that time, the relief from pain/nausea was amazing for me, and also it is such a reliable contraceptive. And now I have periods which are much much better than before in terms of frequency, duration, flow and comfort.
NOTE: Best way to cope with periods is a mooncup! Seriously, no problem with swimming or pretty much anything then.