The biggest problem is that you are keeping the string in way beyond it’s life. Poly goes dead often long before you break them. For competitive player in high school season. You should be restringing polys every 3 weeks at least.

Muiti will hold tension and playability better. But you might lose to much spin and control needed for the modern game.

My best recommendation is for you to get an entry level stringing machine and learn to string yourself. Then you are able to restring every 2-3 weeks at much lower cost.

At last, there are also many polys that holds their playability much better than RPM Blast, playing good for much longer in your frame. Here are some options:

Luxilon 4G: Gold standard of playability duration still, but very stiff. Would recommend stringing at 48 or lower.

Tecnifibre Razor Soft: New String Medvedev just switched to. It’s also a dead string with a ton of control, but more comfortable than 4G. It opens up after the first 30 mins and stay quite consistent then. Should compliment your racquet really well. Since it’s new you might have to order online. I would try 50 lbs.

Tourna Big Hitter Silver 7 Tour Best value string on the market. But the cost advantage doesn’t kick in if you are paying a $18 stringer fee each time, might as well go with the more premium options above. It’s a lighter string that opens up more, so I’d go with the thicker 1.30 gauge for your frame. It’s a shape string with crisp feel. And after some hours it doesn’t stiffen up and dies like many others, but opens up more and gets a bit softer. Try 50lbs or a bit less.

Yonex Poly Tour Rev Has the most pop and pocketing out of my recs. But still provides a predictable string bed, unlike softer polys. Purple or white color should be good for your frame. This string also plays quite similar even towards the end of its life.

Message me on @tenniswziming on IG. I just started sharing some of my string/racquet tests and can answer more questions if you have