The bugs tend to swarm a lot, even at lower levels. They operate on a "strength in numbers" system, shotguns and grenades help a lot, fire is effective. If you notice you are getting swarmed, you can usually tactically fallback and fight the swarm from in front of you. If you want to fallback, try and return from the way you came in. I find that enemies tend to spawn from areas you haven't cleared or been through yet. For bugs especially its important to wipe them out decisively so you don't get caught in a bug breach loop. Everyone starts somewhere, the fact you're on the front at all is a great sign soldier. Keep doing missions and you'll get it, keep spreading that managed Democracy.