given in topical treatment of dermatosis
As you have already used it for 3 weeks, allergic reactions dont seem to be first cause.
But look for bacterial/viral/fungal infections in that region, as betacap can cause exacerbation of same. That might have resulted in rashes.
If rashes continue for sometime again, stop medication and you can see rashes will disappear if it is due to betacap.
If in between you experience severe other symptoms like more rashes /pain/itching; you need to consult dermatologist