I don't think that the pregnancy tests are really accurate enough to compare reliably from today to tomorrow (and definitely not over the course of a day), although if there is a massive increase in hCG you might see a darker line. The only way to be sure what's going on is to get referred to an early pregnancy unit by your GP or midwife (I had a similar situation and phoned my midwife from my previous pregnancy and she referred me - much faster than trying to see my GP!)
However even this won't necessarily help - EPUs will only see you if you think you are 6 weeks (from last period) along or more as scans done earlier than this tend to be inconclusive (6 weeks is the time that a heart beat will be visible in most, but not all, embryos). If you are less than 6 weeks along they will ask you to wait it out.
From what you say it your OP it sounds like you are probably in the more early stages of pregnancy (hence very faint line) and so (unless you experience any pain or discomfort) the "sensible" thing to do is wait a few days and then do another test to see if you have a darker line (although in your shoes I would probably do a test tomorrow, and the next day, and the next day...) If you do get the darker line then definitely get your GP to refer you to the EPU for a dating scan in a couple of weeks.
If you think there is any chance that you could be further along or if you experience any pain (don't wish to worry you but if you aren't familiar with the symptoms of an ectopic pregnancy then look them up - I had a friend with very similar symptoms to yours, except that she didn't know she was pregnant until she was in A&E a few weeks later with an ectopic rupture 
) then you should get a referral to an EPU ASAP.
On the whole does bleeding = a miscarriage front, maybe and maybe not. I experienced bleeding when I thought I was 8 weeks pregnant, then scan wasn't conclusive as they couldn't see anything despite my hCG levels being quite high and I went on to miscarry (as in, without giving TMI, it was clear that the pregnancy had failed) a few days later.
In my next pregnancy I had virtually identical symptoms at around 6 weeks and so didn't hold out much hope, however the scan showed a viable embryo with a heart beat! I continued to bleed (including bright red blood with cramping) for just over two weeks and had a very hard time staying positive, despite having a second scan at 8 weeks showing everything was fine. Well it did work out and DS2 is now nearly 9 months old. 
I still have no idea what caused the bleeding as there was nothing obvious on either of the early scans.
I spent a lot of time online trying to figure out my chances both times but the irritating thing is that ultimately you just have to wait and see... Hope that things work out well for you and that you don't have to wait too long to find out.
PS Don't bother with digital tests - they're a waste of money (and resources)and they're actually less sensitive than supermarket cheapo ones for early pregnancy. 