Slowness & Other Issues After New Battery

So I started experiencing horrible speed issues on my iPhone after the new iOS release(like so many others). Finally heard about the battery issue and took it to Apple Store for a new battery. They gave me the run around(wanted me to wait 3-4 hours and wouldn't let me schedule an appointment, JUST to see if I qualified for the discounted battery, which, once ordered would be in around 4-6 weeks later). So, since I've replaced numerous screens in iphones, I decided to buy my battery from ifixit. Got it installed with no problems although the new sticky strips almost got me down.

I'm still experiencing major issues I was before I switched the battery:

Phone will freeze at random times

When locked, notifications will pop up then disappear

Opening messages app shows messages sent 4 or 5 messages previously

It's really annoying. Is there anything more I can do or am I stuck upgrading my phone? Is it possible I got s bad battery from ifixit? Any advice is greatly appreciated.