Okay, @Imessedp123; it's time to do some growing up and quickly.
1. Your university will have a written drugs policy. Find and read it. My university's blanket policy on drugs was automatic removal from campus accommodation but beyond this - admittedly quite disruptive - punishment they continued as normal on their course.
2. There will be an appeals process. In most universities, the appropriate place to find out about how this works would be your Students' Union. I would contact the appropriate person there first thing on Monday for independent advice about your local processes. They will also know about the university drugs policy and likely response from the police. To be honest, if two security officers and a hall monitor found weed in your room then I suspect there's nothing very much to appeal. That shouldn't stop you contacting the SU for advice, though. Your usual university sources of support (hall monitor, personal tutor, etc) now have a conflict of interest and you might (correctly) feel that you can't confide everything to them.
3. It sounds as if they intend to inform the police. It's likely that there will be a community police officer that is responsible for the campus. If the quantity of marijuana was very small, hopefully they will just visit to talk to you about drugs. I would strongly advise being 100% polite and humble towards this person. Explain that you are a medical student and that this allegation could have a huge impact on your future career but do not allow yourself to be interviewed or admit anything without getting legal advice first. If you can afford it, I would consider talking to a solicitor this weekend so that you understand your position and can deal with police in the event that they visit. Speak to your parents only if you want to or if they are the only way that you can fund a solicitor. Do not under any circumstances do something mad like accept a caution (etc) unless this is following independent legal advice. The police might think that a caution is "letting you off" but this isn't as benign an outcome for you as it might be for other students.
4. Once you can see how this is going to pan out, you should meet with your personal tutor to discuss self-referral to your medical school fitness to practice committee. It is very likely that a FTP committee will let you continue at medical school if you self-refer, take responsibility for your behaviour, and show that it will not happen again. If they find out about this through some other means (which is very possible as it might be routine to inform departments/tutors) then this will make things much more serious than if you are upfront and honest from the beginning. I would only skip this part if there is very clearly going to be no sanction imposed by either the police or the university.
5. Do your work, find some better friends, and don't gamble your career on spins of a roulette wheel. You are not the first medical student (nevermind the first student) to be caught with marijuana and it will work out okay eventually. It's normal to feel upset/stressed/anxious but this will all resolve once you know where (if anywhere) this is all headed.
DOI: Doctor, clinical tutor, and former hall warden.