I had a similar situation as the one you describe... Lumpy, tender... I was very concerned... I thought it might be a hernia or something.
I went to the doc. she said it was swollen lymph nodes... but gave no specific cause (apparently my body was fighting an infection) They went way completely in about 3 weeks. That was 5 years ago and I have not had it happen since.
I would recommend you watch them closely... if they are still there in a few weeks, I'd get them checked out.