It’s great to workout regularly, and if you’re training 5/6 days a week, then you need to make sure you plan in some time for the muscles to recover – which is often why split routines are helpful, because it allows your muscles 24-48 hours to recover.
There are other things you need to do too, remember to replace fluids, if you’ve done a heavy session you will have sweat a lot, and you need to replace that fluid. Checking your urine can help you figure out if you’re dehydrated (if the headache doesn’t), stretch the muscles you worked, eat properly, ideally within an hour of your session, include protein and and carbs (poached egg on wholegrain toast(, if nothing else try a snack (chocolate milk is good on the go).
Rest! Sometimes active recovery – light exercise such as swimming can help aching muscles or DOMS, but sometimes, you just need to stop. Relax, maybe have a sports massage (painful but worth it) or just do nothing – for a few days or longer. It’s good to have a proper break – it allows your body to fully recover, avoid overtraining and means you can come back stronger, and without injury.