after senior year

If i do research and clinical volunteering after my senior year of high school but before my freshman year of college, can I put it on my med school applications?

Yes

You can put whatever you want on your AMCAS application, but you only have a very limit number of slots you can use. (10, IIRC).

Those 10 slots have to cover all honors, awards, shadowing experiences, clinical experiences, community service projects, research experiences, jobs, publications, TA positions, and leadership positions.