Cheesebiscuit,
I do not normally give medical advice online. But in your case I'm afraid I must speak up, because your case is an example of how a misguided search for urgent medical advice can turn deadly. I apologize in advance for my tone, but I am afraid that this issue calls for some firmness, in hopes that such firmness will not only help this post stay in the memory of those who read it, but will guide you to urgent action.
A bruise is blood. Take a look at the size of your bruise, and imagine it's 1-2 cm deep from what you can see. If that amount of blood had left your body, either immediately or over the course of a week, would you have gone on the internet for medical advice, or presented to an emergency room?
Are you confident that anyone on this forum has adequately assessed your bruise? You can see it and feel it. We cannot. Neither you nor anyone on this forum has an ability in an online context to obtain radiologic images, or to place a tube in your abdomen, or to open your abdomen in an operating room/operating theatre, to assess whether or not you are bleeding to death from an internal injury.
Some people on this forum say they may have some medical training, including myself. Do you have any way to verify this? People masquerade as healthcare professionals for all sorts of rational or irrational reasons. In light of this uncertainty, will you place your life in the hands of individuals online by basing your healthcare decisions on assessments of your medical condition made in this forum? Sharing your experience as a patient with others online who have been patients is something for which the internet, and this forum, is a massively powerful tool. Seeking medical advice as to whether or not a condition needs urgent attention is another matter entirely. In short, if you think your condition might or might not require urgent attention, then seek urgent attention.
You have access to emergency care from the NHS in the UK, regardless of your visa status. If you present for a healthcare assessment in the UK, and it turns out you've overreacted, the worst that has happened to you is that you've wasted your time and effort a little. If you don't present for a healthcare assessment, and it turns out you've underreacted, the worst that could potentially could happen to you is a fatal outcome, either sooner or later. The possibility of a fatal outcome for you applies to your case.
From what you are describing, my assessment is the following: there is a moderate possibility you are slowly bleeding to death from a laceration of either your spleen, an abdominal artery, or your liver, or any combination of the three. Such an injury requires emergent intervention, and requires either an intravascular intervention or outright surgery to repair, usually surgery. It is my sincere hope that you see my online assessment as completely without merit with regard to its accuracy, as I have not assessed you in person in any way whatsoever. However, I do hope my assessment has raised some theoretical concern in your mind.
Therefore, if there is any advice you take from this forum, please let it be the following: immediately at the end of reading this sentence, drop everything else you are doing and go to the nearest emergency room as quickly as possible.