Does not show any medicare tax withheld on my check stubs

It will not cause a problem with the IRS.  The amount withheld for Medicare does not go on your tax return.  But you should be asking your employer why they are not withholding for Medicare.  Are they withholding for Social Security?  Is there anything on your pay stub that says "FICA?"

Is  your employer treating you as a W-2 employee or an independent contractor who must pay their own SE tax (Medicare and Social Security)?

Are they taking anything out of your checks like Social Security, FICA, Tax withholding etc?   They might be paying you as an independent contractor and not as an employee.  Ask if you will get a W2 or 1099Misc in January.