Outdoor bugs are never safe, no matter where you live. Even if your area does not spray pesticides, run off from other areas can affect water sources. Gasoline from cars is a pollutant as well. Plus, these bugs carry all sorts of nasty things inside them! If you dont live near enough to a petstore, just order some crickets, or even better silkworms, from offline and keep them at home 
What does the blister look like? Is it just a pocket of air under the skin right by the "armpit"? Look at the other side, is there one there too? If the blister is not red, pussy or open then its probably just a fat pouch, which is another way leos store extra fat...kind of like they do in their tails 
As far as being sluggish...check all your temps and run a fecal. If everything is ok and he is still actuing strange or isnt eating much then i would take him to the vet
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0.1 Bearded dragon (Hannabil)
0.1 mexican Black kingsnake (Morticia)
1.1.2 Leopard Gecko's (Pogo, Louise, Orion, Jeffrey Nothing)
0.0.1 Tokay Gecko
1.0 Blue Tongue Skink
0.0.1 Reverse Okeetee Corn (Autumn)
0.1 Bullmastiff (Asha)
4.1 Cats (Poe, Tucker, Abhid, Felicity, Emmy)