Hello sir ... I'm 17 ...

I had my first and last intercourse on 3rd jan this year and then I hve missed my periods Nd the date was 28th ....We had first time without protection but their was no insertion of cum inside...Nd then used condoms...Nd after 3 hours had an ipill...

I hve checked pregnancy tests via prega news.. Nd other homemade ways but all shows a negative result .... 

So can u plzz tell me y I'm not getting periods ...Is there any reason to run to gynaecologist...Or it is simply the side effect..