What could be causing achy, lumpy pain under both breasts near armpits?

After the intercourse if you had periods in March, April, and May, on March 5th, it's unlikely that you're pregnant, as regular periods suggest otherwise.

I understand that you are concerned that you could be pregnant after unprotected sex on May 19 following your period on April 25. Let me tell you this: yes, you can get pregnant as the sperm can stay alive in a woman’s body for several days. Take a pregnancy test if you miss your period, have nausea, or feel tenderness in your breasts. 

Its absolutely normal for periods to get delayed by few days or so. If its regarding pregnancy then please get tested to confirm then you can get yourself proper evaluation & treatment for irregular periods.

When you take Normens tablets longer than the prescribed 21 days, it may cause hormonal imbalance. An extended use of 25 days will not greatly affect your AMH level. However, it’s better to follow the recommended period to prevent any possible dangers.

If you feel pain or burning sensation during urination and have taken a pregnancy test yet see no lines then visiting the doctor is advised. An r gynecologist can offer appropriate diagnosis and treatment plan whenever necessary. Further, you should continue taking your prescribed medication for the UTI in order to maintain a healthy life.