Mixing meth and poppers won't cause any kind of interaction, however you need to be careful when doing any kind of stimulants. It is possible to overdose on meth, which can cause any number of things, including sudden cardiac arrest.
As well, it should be noted that meth can make a person stay awake for an abnormal amount of time (even days at a time). This in and of itself is rather unhealthy and can cause a wide variety of unpleasant things to happen, such as memory issues, micro sleeps, and even involuntarily revealing information you may not necessarily want to be revealed, without having any conscious recollection of doing so.
As for the meth itself, I should warn you that there is a new rising issue (at least here in Canada) whereas the meth is more and more often laced with something like Fentanyl, which even in small doses, can be fatal. For these reasons, I would strongly recommend that you stick to just the poppers.