I think it's sorer with the lighter weights because later when the muscles, ligaments and tendons are warmed up the pain's temporarily masked.
I think you should take a week completely off, after first trying to do exercises that will allow the area to heal without directly aggrevating. Once the pain's gone, you might have to consider slight changes to the program that will avoid further aggrevation that might otherwise return. For example any areas that have been injured might be subject to moderate reps no lower than 10-15 in future, rather than lower reps with heavier weight that is harder on the joints. Combine that with shorter rests of no more than a minute between sets, to keep the area warm.
If after taking a break the pain's still there, then see a doctor it may be slightly more serious.
When the problem is cured, ensure that with whatever exercise(s) caused it, there is thorough warmup and that reps are kept 10-15 in future, with rests of no longer than a minute, to keep the area warm.
If all that still doesn't help, you may have to first try slight modifications of the exercise(s)/ROMs that might not irritate, such as different grips, grip widths and/or the use of dumbbells in lieu of barbells. If that's insufficient to remove the problems, then find alternate exercises that don't cause the pain. You'll have to find way to avoid further similar aggrevations as they'll only get worse if they return.
