Thanks for posting your query at DoctorSpring.com
You maybe pulled a muscle while lifting the heavy weight.
It is most advisable to refrain from lifting heavy weights, straining unnecessarily or bending during early pregnancy, particularly so, after an IVF ( a precious pregnancy in every sense ).
Since there is no bleeding, there is no reason to assume the worst.
Take bedrest, you can take a solitary painkiller.
IF the pain is not gone after 12 hours, see your doctor.
Also, yes, HCG is not reliable for establishing the successful progression of a pregnancy.
It is best to go in for a pelvic transvaginal ultrasound scan.
All the best
PLease feel free to discuss further.