Don't get too concerned. Some discharge is normal. In a healthy relationship I don't think it's a problem joking about it, better than your boyfriend being put off by it. Nothing to suggest any particular colour means you're pregnant.
Your GP can send you to see a specialist if nessasary, but I suspect things may be normal for you and the increased discharge may just represent you moving to unprotected sex and your vagina having more foreign semen to remove through it's normal cleaning processes. That said getting infection ruled out is wise. Increased sexual activity is a risk for STIs but also other infections like thrush and bacterial infections.
Nothing to worry about.
One thought - you've not moved to more 'sexy' underwear? Cotton is supposidly the most healthy material and things can breath