Could be a couple of things:
1. As previously mentioned, overheating. Make sure intake and exhaust ports are unobstructed and dust free. Take some canned compressed air and plow out heat sinks and fans. Ensure that intake/exhaust ports have clearance for airflow.
2. Laptops can have bloat ware, manufacturers utilities, or OS settings which favor power saving (for battery) over performance. Make sure things are set for performance.
3. Update OS patches, update drivers
4. If you’ve got a brand name laptop, do some searching to see if they have weird issues like thermal paste on cpu/gpu.
5. Some laptops have on board gpu which shares system RAM and cpu resources, plus a separate graphics card, check to make sure you’re using gpu card for gaming
if it just started happening, I’d suspect gpu cooling issues and/or OS/hardware patches/hot fix/updates.