Treacle - I'm fairly sure Sebsmum mentioned a pregnancy after mc thread on here a few weeks ago, so it might be worth sending her a PM so that you can locate it, as there may be people on there who've experienced something similar.
If you're concerned about the pain you're experiencing, then I would definitely give NHS direct a call/ call a doctor for advice. An EPU is probably best placed to advise, although I'm conscious that it varies from hospital to hospital as to whether you can self refer or not and indeed, whether they're open on a weekend. In terms of what treatment they can offer you, based on my experience of what my local EPU does, I assume an EPU would take bloods to check whether your hcg levels are doubling, and although they can scan you from around 4 weeks, I don't think a scan is likely to be definitive until around 5 weeks.
If it gives you any comfort, I didn't have any one sided pain with my ruptured ectopic, although I'm conscious everyone is different. My only real symptoms up until 5 weeks were spotting (ond and off) and the fact that my hcg levels didn't seem to be going up as they should.
That having been said, It sounds to me as though it's definitely worth you discussing your pains with someone who can give medical advice this weekend.