When to take a pt?

How long after ur first unprotected sex should u take a test? I came off implanon the 25th march & had first unprotected sex the 27th march and upto 4 times a week since then! When should I take a test I've took a few since then but all say negative. I know it's way to early to know but need some advice should I wait until I'm back my holiday on 13th May to take a first response one as I'm only using the cheap ones off eBay?