Can I do a PhD without MSc?
Some places in continental Europe can accept people with BSc but without MSc (but most - don't). In UK and US, MSc is a part of PhD, so typically you do don't need one to start.

But you ALWAYS need to consult a particular university/institute, as rules vary (and especially with treating foreign diplomas).

However, if your "GPA sucks" then, unless you have a strong research track (i.e. strong recommendation letters from your research internships, published papers) special exceptions may by unlikely.