Fainter line on second test?

My husband and I just had our first baby, a daughter in August. We’ve not been actively trying... just enjoying each other. Well I was 6 days late and finally decided to test last night. We got a positive! We are both stunned and happy that this happened naturally for us after a 2 year battle with infertility before our daughter was born. Well I tested again this morning out of pure excitement, and it’s 2 lines but the second line is much fainter than it was last night. Should I be worried? I know 2 lines is a positive result but after our struggles it’s hard not to worry. Looking for reassurance. Planning on calling and making an appointment on Monday as the offices are closed on Sundays.