You don't have to have a transvaginal scan. If they know you've never been sexually active they'll be patient and do an external ultrasound and use it to the best of their ability to see enough to diagnose or exclude anything. Your friends shouldn't have advised to lie. Gynae problems strike before you ever have sex sometimes so they'd still have taken you seriously but it would have been easier to exclude STIs etc. and would have given them information to be more gentle with you as someone who is inexperienced.

I had gynae problems before sexual activity but it wasn't cancer. Don't worry that your symptoms are that before other things have been excluded. There's loads of things that can cause irregular periods or any number of symptoms. You haven't said what you have been experiencing but it seems your doctor is being attentive. I can't tell you how important it is to be honest about not wanting a transvaginal scan. It's not too uncomfortable but shouldn't be your first penetrative experience. You don't need that.