Can an lp cause meningitis? what to watch out for? or is it just a spinal headache

In theory-yes: If you have blood poisoning (sepsis) & the germs were allowed into the spinal fluid during a bloody tap, in theory you could develop meningitis from that process. In reality you would likely be dead from the sepsis before your spinal fluid infection became evident. If you have a headache it is likely just from spinal fluid leakage & a blood patch may be needed to stop it.