Let me start by saying I am not a trained medical professional or pharmacist. Use advice at own risk.
You could also try taking antidepressants that are under the Selective Serotonin Reuptake Inhibitor (SSRI), most famous and easily available is Prozac, or generic name fluxotine. I read somewhere that unless you're actually depressed and need the drug to regulate your serotonin, popping one was it... 6 hours or something before, makes it harder to cum. If you want some, just tell your doctor you've been feeling depressed and they prescribe it like candy because too many "depression" cases aren't clinical, they're just "you're feeling a bit down, your parents would've just gone to the pub to get pissed and cheer up" type.
If you cum too fast, could just be you're suffering from performance anxiety due to date being sizzling hottie, and worrying about cumming too fast. Try meditation to calm yourself down, so you can slow down and take it easy and enjoy physical intimacy.
Or just cheat and take a sedative, like diazepam, trade name Valium. If you're not already using it, one 10mg pill should be enough for someone 13 stone without making you TOO chilled and unable to get hard. Again, since it's safe and not strong, all you need to do is just say you've been having some anxiety, and trouble sleeping, and a doc should just prescribe you some to "try to see if it helps." For reference, if you're actually having a panic attack that you actually need to go to A&E for, they give you three 10mg pills right away, probably crushed to avoid the slow release effect and THEN bring out the stronger drugs.
