the drug zeros your libido and stops the production of any natural lubrication down below. So my first thought is that without that, if you didn't add copious amounts of lube, you have probably done yourself a mischief down below.
If the bleed is very fresh red blood then that would indicate injury rather than a period. If your bleed is dark brownish sludge then that is an actual period. The menstrual lining not having slewed out for a while due to the drugs will have turned dark brown by now, and if it is a genuine period and the menstrual lining is shedding away then the colour should be significantly different from a fresh blood red bleed.
If that makes sense.
If it is an injury bleed then you are going to either have to give the penetrative sex a miss and try something else, or use plenty lube and top up as you go at it.
Your body normally produces enough to keep things working well, but on the drug it gets very dry down below and will be prone to tearing or injury to any adhesions that you had and that can cause the bleeding.
Another reminder incase you hadn't read the patient advice leaflet. BC pills do not work when you are on zoladex. And Zoladex is toxic to a developing baby. So the last thing you want to do is accidentally get pregnant while any of the drug is still in you.
Therefore must use barrier contraception, diaphragm and/or condoms every time....plus the extra lubrication.
And the drug residue remain inside you for 4 months after each implant (enough to damage a baby but not to stop your ovaries working.) so while there is the remote chance the drug remains you should avoid getting pregnant if at all possible.
You probably knew that, but in case anyone else reads this who didn't know it, that is the situation regarding sex and zoladex.
If you have had a proper period, then two things could be the cause. first the implant could have failed you this month, and second your activities in the bedroom triggered the uterus lining to tear away . Same can happen after extreme exercising or accidental injury to the tummy even when not on zoladex.
Regardless of what triggered the bleed, i hope it's over for you soon, and you can perhaps consider trying other activities in the bedroom that won't injure you inside when you are in a fragile state.